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 $133.56   7.733%   $143.8882   $143.89   $143.90   $143.90  
  Purchase #2 $94.60   8.730%   $102.8586   $102.86   $102.85   $102.90  
  Purchase #3 $97.96   3.127%   $101.0232   $101.02   $101.00   $101.00  
  Purchase #4 $14.73   11.112%   $16.3668   $16.37   $16.35   $16.40  
  Purchase #5 $170.37   4.470%   $177.9855   $177.99   $178.00   $178.00  
  Purchase #6 $7.56   7.136%   $8.0995   $8.10   $8.10   $8.10  
  Purchase #7 $249.62   6.470%   $265.7704   $265.77   $265.75   $265.80  
  7 purchase totals = $768.40       $815.9922   $816.00   $815.95   $816.10