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 $92.65   4.721%   $97.024   $97.02   $97.00   $97.00  
  Purchase #2 $227.68   12.190%   $255.4342   $255.43   $255.45   $255.40  
  Purchase #3 $114.56   9.485%   $125.426   $125.43   $125.45   $125.40  
  Purchase #4 $31.84   7.275%   $34.1564   $34.16   $34.15   $34.20  
  Purchase #5 $170.43   9.802%   $187.1355   $187.14   $187.15   $187.10  
  Purchase #6 $95.78   12.792%   $108.0322   $108.03   $108.05   $108.00  
  Purchase #7 $70.45   4.834%   $73.8556   $73.86   $73.85   $73.90  
  7 purchase totals = $803.39       $881.0639   $881.07   $881.10   $881.00