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 $60.43   4.136%   $62.9294   $62.93   $62.95   $62.90  
  Purchase #2 $138.73   9.758%   $152.2673   $152.27   $152.25   $152.30  
  Purchase #3 $91.37   4.664%   $95.6315   $95.63   $95.65   $95.60  
  Purchase #4 $57.62   11.335%   $64.1512   $64.15   $64.15   $64.20  
  Purchase #5 $67.79   9.665%   $74.3419   $74.34   $74.35   $74.30  
  Purchase #6 $224.39   9.414%   $245.5141   $245.51   $245.50   $245.50  
  Purchase #7 $136.46   9.820%   $149.8604   $149.86   $149.85   $149.90  
  7 purchase totals = $776.79       $844.6958   $844.69   $844.70   $844.70