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 $46.65   10.522%   $51.5585   $51.56   $51.55   $51.60  
  Purchase #2 $91.43   4.347%   $95.4045   $95.40   $95.40   $95.40  
  Purchase #3 $107.68   8.627%   $116.9696   $116.97   $116.95   $117.00  
  Purchase #4 $46.26   10.817%   $51.2639   $51.26   $51.25   $51.30  
  Purchase #5 $245.53   12.407%   $275.9929   $275.99   $276.00   $276.00  
  Purchase #6 $78.32   13.749%   $89.0882   $89.09   $89.10   $89.10  
  Purchase #7 $40.75   10.560%   $45.0532   $45.05   $45.05   $45.10  
  7 purchase totals = $656.62       $725.3308   $725.32   $725.30   $725.50