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 $7.76   3.372%   $8.0217   $8.02   $8.00   $8.00  
  Purchase #2 $190.64   4.607%   $199.4228   $199.42   $199.40   $199.40  
  Purchase #3 $199.61   9.551%   $218.6748   $218.67   $218.65   $218.70  
  Purchase #4 $56.46   7.742%   $60.8311   $60.83   $60.85   $60.80  
  Purchase #5 $144.30   10.156%   $158.9551   $158.96   $158.95   $159.00  
  Purchase #6 $143.44   7.460%   $154.1406   $154.14   $154.15   $154.10  
  Purchase #7 $127.31   9.522%   $139.4325   $139.43   $139.45   $139.40  
  7 purchase totals = $869.52       $939.4786   $939.47   $939.45   $939.40