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 $222.57   8.393%   $241.2503   $241.25   $241.25   $241.30  
  Purchase #2 $96.54   5.622%   $101.9675   $101.97   $101.95   $102.00  
  Purchase #3 $46.80   7.560%   $50.3381   $50.34   $50.35   $50.30  
  Purchase #4 $201.90   11.828%   $225.7807   $225.78   $225.80   $225.80  
  Purchase #5 $187.57   13.166%   $212.2655   $212.27   $212.25   $212.30  
  Purchase #6 $9.46   10.512%   $10.4544   $10.45   $10.45   $10.50  
  Purchase #7 $42.63   8.596%   $46.2945   $46.29   $46.30   $46.30  
  7 purchase totals = $807.47       $888.3510   $888.35   $888.35   $888.50