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 $245.95   6.389%   $261.6637   $261.66   $261.65   $261.70  
  Purchase #2 $210.47   4.316%   $219.5539   $219.55   $219.55   $219.60  
  Purchase #3 $44.88   4.666%   $46.9741   $46.97   $46.95   $47.00  
  Purchase #4 $69.60   11.569%   $77.652   $77.65   $77.65   $77.70  
  Purchase #5 $10.35   5.559%   $10.9254   $10.93   $10.95   $10.90  
  Purchase #6 $118.33   6.817%   $126.3966   $126.40   $126.40   $126.40  
  Purchase #7 $226.79   7.631%   $244.0963   $244.10   $244.10   $244.10  
  7 purchase totals = $926.37       $987.2620   $987.26   $987.25   $987.40