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 $234.34   13.518%   $266.0181   $266.02   $266.00   $266.00  
  Purchase #2 $51.58   11.229%   $57.3719   $57.37   $57.35   $57.40  
  Purchase #3 $194.53   12.213%   $218.2879   $218.29   $218.30   $218.30  
  Purchase #4 $89.93   5.804%   $95.1495   $95.15   $95.15   $95.10  
  Purchase #5 $47.86   4.483%   $50.0056   $50.01   $50.00   $50.00  
  Purchase #6 $222.34   6.449%   $236.6787   $236.68   $236.70   $236.70  
  Purchase #7 $24.71   13.386%   $28.0177   $28.02   $28.00   $28.00  
  7 purchase totals = $865.29       $951.5294   $951.54   $951.50   $951.50