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 $59.65   3.147%   $61.5272   $61.53   $61.55   $61.50  
  Purchase #2 $151.41   4.334%   $157.9721   $157.97   $157.95   $158.00  
  Purchase #3 $16.87   13.363%   $19.1243   $19.12   $19.10   $19.10  
  Purchase #4 $131.46   6.836%   $140.4466   $140.45   $140.45   $140.40  
  Purchase #5 $209.82   9.137%   $228.9913   $228.99   $229.00   $229.00  
  Purchase #6 $32.30   9.485%   $35.3637   $35.36   $35.35   $35.40  
  Purchase #7 $236.77   10.355%   $261.2875   $261.29   $261.30   $261.30  
  7 purchase totals = $838.28       $904.7127   $904.71   $904.70   $904.70