Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $236.45   4.634%   $247.4071   $247.41   $247.40   $247.40  
  Purchase #2 $183.51   10.571%   $202.9088   $202.91   $202.90   $202.90  
  Purchase #3 $225.42   11.212%   $250.6941   $250.69   $250.70   $250.70  
  Purchase #4 $167.63   11.835%   $187.469   $187.47   $187.45   $187.50  
  Purchase #5 $236.85   9.120%   $258.4507   $258.45   $258.45   $258.50  
  Purchase #6 $146.43   4.431%   $152.9183   $152.92   $152.90   $152.90  
  Purchase #7 $159.61   10.790%   $176.8319   $176.83   $176.85   $176.80  
  7 purchase totals = $1,355.90       $1,476.6799   $1,476.68   $1,476.65   $1,476.70