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 $66.95   13.118%   $75.7325   $75.73   $75.75   $75.70  
  Purchase #2 $48.50   13.662%   $55.1261   $55.13   $55.15   $55.10  
  Purchase #3 $221.82   6.821%   $236.9503   $236.95   $236.95   $237.00  
  Purchase #4 $164.38   4.161%   $171.2199   $171.22   $171.20   $171.20  
  Purchase #5 $153.41   8.768%   $166.861   $166.86   $166.85   $166.90  
  Purchase #6 $66.30   10.861%   $73.5008   $73.50   $73.50   $73.50  
  Purchase #7 $114.85   6.689%   $122.5323   $122.53   $122.55   $122.50  
  7 purchase totals = $836.21       $901.9229   $901.92   $901.95   $901.90