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 $47.37   4.395%   $49.4519   $49.45   $49.45   $49.50  
  Purchase #2 $228.84   8.126%   $247.4355   $247.44   $247.45   $247.40  
  Purchase #3 $67.29   11.191%   $74.8204   $74.82   $74.80   $74.80  
  Purchase #4 $114.62   8.685%   $124.5747   $124.57   $124.55   $124.60  
  Purchase #5 $227.97   13.502%   $258.7505   $258.75   $258.75   $258.80  
  Purchase #6 $196.81   5.597%   $207.8255   $207.83   $207.85   $207.80  
  Purchase #7 $62.29   3.417%   $64.4184   $64.42   $64.40   $64.40  
  7 purchase totals = $945.19       $1,027.2769   $1,027.28   $1,027.25   $1,027.30