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 $82.87   13.403%   $93.9771   $93.98   $94.00   $94.00  
  Purchase #2 $167.69   6.462%   $178.5261   $178.53   $178.55   $178.50  
  Purchase #3 $48.40   13.522%   $54.9446   $54.94   $54.95   $54.90  
  Purchase #4 $6.96   11.137%   $7.7351   $7.74   $7.75   $7.70  
  Purchase #5 $250.67   6.468%   $266.8833   $266.88   $266.90   $266.90  
  Purchase #6 $87.43   11.521%   $97.5028   $97.50   $97.50   $97.50  
  Purchase #7 $231.99   7.727%   $249.9159   $249.92   $249.90   $249.90  
  7 purchase totals = $876.01       $949.4849   $949.49   $949.55   $949.40