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 $56.39   8.586%   $61.2316   $61.23   $61.25   $61.20  
  Purchase #2 $27.48   4.546%   $28.7292   $28.73   $28.75   $28.70  
  Purchase #3 $249.38   7.465%   $267.9962   $268.00   $268.00   $268.00  
  Purchase #4 $45.51   9.449%   $49.8102   $49.81   $49.80   $49.80  
  Purchase #5 $13.33   4.335%   $13.9079   $13.91   $13.90   $13.90  
  Purchase #6 $249.68   5.255%   $262.8007   $262.80   $262.80   $262.80  
  Purchase #7 $73.84   10.302%   $81.447   $81.45   $81.45   $81.40  
  7 purchase totals = $715.61       $765.9228   $765.93   $765.95   $765.80