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 $141.89   4.246%   $147.9146   $147.91   $147.90   $147.90  
  Purchase #2 $218.95   12.150%   $245.5524   $245.55   $245.55   $245.60  
  Purchase #3 $159.28   10.108%   $175.38   $175.38   $175.40   $175.40  
  Purchase #4 $64.35   4.603%   $67.312   $67.31   $67.30   $67.30  
  Purchase #5 $179.68   6.621%   $191.5766   $191.58   $191.60   $191.60  
  Purchase #6 $168.95   6.493%   $179.9199   $179.92   $179.90   $179.90  
  Purchase #7 $236.63   9.197%   $258.3929   $258.39   $258.40   $258.40  
  7 purchase totals = $1,169.73       $1,266.0484   $1,266.04   $1,266.05   $1,266.10