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 $62.80   5.673%   $66.3626   $66.36   $66.35   $66.40  
  Purchase #2 $205.82   9.144%   $224.6402   $224.64   $224.65   $224.60  
  Purchase #3 $114.63   3.526%   $118.6719   $118.67   $118.65   $118.70  
  Purchase #4 $17.88   7.749%   $19.2655   $19.27   $19.25   $19.30  
  Purchase #5 $89.87   10.717%   $99.5014   $99.50   $99.50   $99.50  
  Purchase #6 $238.25   8.393%   $258.2463   $258.25   $258.25   $258.20  
  Purchase #7 $226.38   10.185%   $249.4368   $249.44   $249.45   $249.40  
  7 purchase totals = $955.63       $1,036.1247   $1,036.13   $1,036.10   $1,036.10