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 $222.32   11.361%   $247.5778   $247.58   $247.60   $247.60  
  Purchase #2 $121.89   3.306%   $125.9197   $125.92   $125.90   $125.90  
  Purchase #3 $158.51   10.714%   $175.4928   $175.49   $175.50   $175.50  
  Purchase #4 $107.95   3.774%   $112.024   $112.02   $112.00   $112.00  
  Purchase #5 $188.25   4.797%   $197.2804   $197.28   $197.30   $197.30  
  Purchase #6 $15.56   11.166%   $17.2974   $17.30   $17.30   $17.30  
  Purchase #7 $114.90   11.550%   $128.171   $128.17   $128.15   $128.20  
  7 purchase totals = $929.38       $1,003.7631   $1,003.76   $1,003.75   $1,003.80