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 $231.42   5.851%   $244.9604   $244.96   $244.95   $245.00  
  Purchase #2 $116.80   10.853%   $129.4763   $129.48   $129.50   $129.50  
  Purchase #3 $158.63   10.628%   $175.4892   $175.49   $175.50   $175.50  
  Purchase #4 $207.87   4.302%   $216.8126   $216.81   $216.80   $216.80  
  Purchase #5 $57.51   8.725%   $62.5277   $62.53   $62.55   $62.50  
  Purchase #6 $227.32   11.477%   $253.4095   $253.41   $253.40   $253.40  
  Purchase #7 $215.71   11.820%   $241.2069   $241.21   $241.20   $241.20  
  7 purchase totals = $1,215.26       $1,323.8826   $1,323.89   $1,323.90   $1,323.90