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 $39.70   11.552%   $44.2861   $44.29   $44.30   $44.30  
  Purchase #2 $189.77   13.425%   $215.2466   $215.25   $215.25   $215.20  
  Purchase #3 $200.78   7.675%   $216.1899   $216.19   $216.20   $216.20  
  Purchase #4 $42.77   7.643%   $46.0389   $46.04   $46.05   $46.00  
  Purchase #5 $34.64   9.530%   $37.9412   $37.94   $37.95   $37.90  
  Purchase #6 $240.93   3.753%   $249.9721   $249.97   $249.95   $250.00  
  Purchase #7 $152.82   6.531%   $162.8007   $162.80   $162.80   $162.80  
  7 purchase totals = $901.41       $972.4755   $972.48   $972.50   $972.40