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 $81.66   13.841%   $92.9626   $92.96   $92.95   $93.00  
  Purchase #2 $32.96   13.103%   $37.2787   $37.28   $37.30   $37.30  
  Purchase #3 $232.82   10.228%   $256.6328   $256.63   $256.65   $256.60  
  Purchase #4 $54.53   8.109%   $58.9518   $58.95   $58.95   $59.00  
  Purchase #5 $190.70   13.137%   $215.7523   $215.75   $215.75   $215.80  
  Purchase #6 $108.67   5.376%   $114.5121   $114.51   $114.50   $114.50  
  Purchase #7 $24.37   11.262%   $27.1145   $27.11   $27.10   $27.10  
  7 purchase totals = $725.71       $803.2048   $803.19   $803.20   $803.30