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 $58.47   6.829%   $62.4629   $62.46   $62.45   $62.50  
  Purchase #2 $88.96   8.314%   $96.3561   $96.36   $96.35   $96.40  
  Purchase #3 $88.97   9.137%   $97.0992   $97.10   $97.10   $97.10  
  Purchase #4 $199.73   4.447%   $208.612   $208.61   $208.60   $208.60  
  Purchase #5 $26.43   8.494%   $28.675   $28.68   $28.70   $28.70  
  Purchase #6 $44.86   7.816%   $48.3663   $48.37   $48.35   $48.40  
  Purchase #7 $69.99   13.370%   $79.3477   $79.35   $79.35   $79.30  
  7 purchase totals = $577.41       $620.9192   $620.93   $620.90   $621.00