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 $75.88   9.337%   $82.9649   $82.96   $82.95   $83.00  
  Purchase #2 $116.85   12.824%   $131.8348   $131.83   $131.85   $131.80  
  Purchase #3 $185.71   7.324%   $199.3114   $199.31   $199.30   $199.30  
  Purchase #4 $126.89   7.797%   $136.7836   $136.78   $136.80   $136.80  
  Purchase #5 $244.53   12.534%   $275.1794   $275.18   $275.20   $275.20  
  Purchase #6 $229.65   10.326%   $253.3637   $253.36   $253.35   $253.40  
  Purchase #7 $140.51   11.227%   $156.2851   $156.29   $156.30   $156.30  
  7 purchase totals = $1,120.02       $1,235.7229   $1,235.71   $1,235.75   $1,235.80