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 $39.93   11.265%   $44.4281   $44.43   $44.45   $44.40  
  Purchase #2 $218.37   10.202%   $240.6481   $240.65   $240.65   $240.60  
  Purchase #3 $120.56   4.590%   $126.0937   $126.09   $126.10   $126.10  
  Purchase #4 $17.32   5.379%   $18.2516   $18.25   $18.25   $18.30  
  Purchase #5 $100.41   10.728%   $111.182   $111.18   $111.20   $111.20  
  Purchase #6 $162.72   8.294%   $176.216   $176.22   $176.20   $176.20  
  Purchase #7 $73.72   4.306%   $76.8944   $76.89   $76.90   $76.90  
  7 purchase totals = $733.03       $793.7139   $793.71   $793.75   $793.70