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 $64.40   13.376%   $73.0141   $73.01   $73.00   $73.00  
  Purchase #2 $232.34   12.315%   $260.9527   $260.95   $260.95   $261.00  
  Purchase #3 $148.58   7.121%   $159.1604   $159.16   $159.15   $159.20  
  Purchase #4 $52.27   5.253%   $55.0157   $55.02   $55.00   $55.00  
  Purchase #5 $56.30   7.354%   $60.4403   $60.44   $60.45   $60.40  
  Purchase #6 $107.46   12.161%   $120.5282   $120.53   $120.55   $120.50  
  Purchase #7 $19.96   11.749%   $22.3051   $22.31   $22.30   $22.30  
  7 purchase totals = $681.31       $751.4165   $751.42   $751.40   $751.40