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 $55.99   11.391%   $62.3678   $62.37   $62.35   $62.40  
  Purchase #2 $238.84   7.489%   $256.7267   $256.73   $256.75   $256.70  
  Purchase #3 $197.42   10.770%   $218.6821   $218.68   $218.70   $218.70  
  Purchase #4 $44.56   8.277%   $48.2482   $48.25   $48.25   $48.20  
  Purchase #5 $67.82   11.857%   $75.8614   $75.86   $75.85   $75.90  
  Purchase #6 $84.48   11.818%   $94.4638   $94.46   $94.45   $94.50  
  Purchase #7 $47.30   5.723%   $50.007   $50.01   $50.00   $50.00  
  7 purchase totals = $736.41       $806.3570   $806.36   $806.35   $806.40