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 $243.69   9.771%   $267.5009   $267.50   $267.50   $267.50  
  Purchase #2 $224.66   5.337%   $236.6501   $236.65   $236.65   $236.70  
  Purchase #3 $53.35   9.399%   $58.3644   $58.36   $58.35   $58.40  
  Purchase #4 $46.86   10.675%   $51.8623   $51.86   $51.85   $51.90  
  Purchase #5 $131.84   12.849%   $148.7801   $148.78   $148.80   $148.80  
  Purchase #6 $19.93   3.451%   $20.6178   $20.62   $20.60   $20.60  
  Purchase #7 $136.63   6.354%   $145.3115   $145.31   $145.30   $145.30  
  7 purchase totals = $856.96       $929.0871   $929.08   $929.05   $929.20