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 $74.35   13.730%   $84.5583   $84.56   $84.55   $84.60  
  Purchase #2 $136.68   6.607%   $145.7104   $145.71   $145.70   $145.70  
  Purchase #3 $191.26   13.837%   $217.7246   $217.72   $217.70   $217.70  
  Purchase #4 $238.47   9.297%   $260.6406   $260.64   $260.65   $260.60  
  Purchase #5 $33.28   6.480%   $35.4365   $35.44   $35.45   $35.40  
  Purchase #6 $121.40   9.109%   $132.4583   $132.46   $132.45   $132.50  
  Purchase #7 $88.91   13.872%   $101.2436   $101.24   $101.25   $101.20  
  7 purchase totals = $884.35       $977.7723   $977.77   $977.75   $977.70