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 $244.25   6.521%   $260.1775   $260.18   $260.20   $260.20  
  Purchase #2 $179.96   7.398%   $193.2734   $193.27   $193.25   $193.30  
  Purchase #3 $198.39   3.797%   $205.9229   $205.92   $205.90   $205.90  
  Purchase #4 $178.39   10.460%   $197.0496   $197.05   $197.05   $197.00  
  Purchase #5 $223.85   9.440%   $244.9814   $244.98   $245.00   $245.00  
  Purchase #6 $244.74   4.687%   $256.211   $256.21   $256.20   $256.20  
  Purchase #7 $127.54   5.177%   $134.1427   $134.14   $134.15   $134.10  
  7 purchase totals = $1,397.12       $1,491.7585   $1,491.75   $1,491.75   $1,491.70