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 $51.58   10.515%   $57.0036   $57.00   $57.00   $57.00  
  Purchase #2 $119.73   5.537%   $126.3595   $126.36   $126.35   $126.40  
  Purchase #3 $33.67   3.241%   $34.7612   $34.76   $34.75   $34.80  
  Purchase #4 $8.83   7.164%   $9.4626   $9.46   $9.45   $9.50  
  Purchase #5 $53.46   12.324%   $60.0484   $60.05   $60.05   $60.00  
  Purchase #6 $190.90   7.366%   $204.9617   $204.96   $204.95   $205.00  
  Purchase #7 $236.82   4.570%   $247.6427   $247.64   $247.65   $247.60  
  7 purchase totals = $694.99       $740.2397   $740.23   $740.20   $740.30