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 $25.71   3.874%   $26.706   $26.71   $26.70   $26.70  
  Purchase #2 $156.84   7.476%   $168.5654   $168.57   $168.55   $168.60  
  Purchase #3 $236.63   5.634%   $249.9617   $249.96   $249.95   $250.00  
  Purchase #4 $123.60   5.351%   $130.2138   $130.21   $130.20   $130.20  
  Purchase #5 $214.76   8.187%   $232.3424   $232.34   $232.35   $232.30  
  Purchase #6 $70.95   7.323%   $76.1457   $76.15   $76.15   $76.10  
  Purchase #7 $108.47   3.326%   $112.0777   $112.08   $112.10   $112.10  
  7 purchase totals = $936.96       $996.0127   $996.02   $996.00   $996.00