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 $211.70   8.282%   $229.233   $229.23   $229.25   $229.20  
  Purchase #2 $131.44   11.212%   $146.1771   $146.18   $146.20   $146.20  
  Purchase #3 $70.51   8.164%   $76.2664   $76.27   $76.25   $76.30  
  Purchase #4 $12.94   11.780%   $14.4643   $14.46   $14.45   $14.50  
  Purchase #5 $126.43   7.847%   $136.351   $136.35   $136.35   $136.40  
  Purchase #6 $215.70   13.414%   $244.634   $244.63   $244.65   $244.60  
  Purchase #7 $114.33   10.144%   $125.9276   $125.93   $125.95   $125.90  
  7 purchase totals = $883.05       $973.0534   $973.05   $973.10   $973.10