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 $40.76   13.567%   $46.2899   $46.29   $46.30   $46.30  
  Purchase #2 $158.42   10.410%   $174.9115   $174.91   $174.90   $174.90  
  Purchase #3 $8.89   8.597%   $9.6543   $9.65   $9.65   $9.70  
  Purchase #4 $28.76   6.422%   $30.607   $30.61   $30.60   $30.60  
  Purchase #5 $91.56   3.709%   $94.956   $94.96   $94.95   $95.00  
  Purchase #6 $103.82   9.311%   $113.4867   $113.49   $113.50   $113.50  
  Purchase #7 $34.92   12.549%   $39.3021   $39.30   $39.30   $39.30  
  7 purchase totals = $467.13       $509.2075   $509.21   $509.20   $509.30