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 $171.73   13.858%   $195.5283   $195.53   $195.55   $195.50  
  Purchase #2 $250.25   10.197%   $275.768   $275.77   $275.75   $275.80  
  Purchase #3 $232.27   7.444%   $249.5602   $249.56   $249.55   $249.60  
  Purchase #4 $30.30   7.377%   $32.5352   $32.54   $32.55   $32.50  
  Purchase #5 $58.44   4.792%   $61.2404   $61.24   $61.25   $61.20  
  Purchase #6 $190.25   9.763%   $208.8241   $208.82   $208.80   $208.80  
  Purchase #7 $232.34   6.431%   $247.2818   $247.28   $247.30   $247.30  
  7 purchase totals = $1,165.58       $1,270.7380   $1,270.74   $1,270.75   $1,270.70