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 $59.95   4.160%   $62.4439   $62.44   $62.45   $62.40  
  Purchase #2 $232.53   3.377%   $240.3825   $240.38   $240.40   $240.40  
  Purchase #3 $69.63   5.193%   $73.2459   $73.25   $73.25   $73.20  
  Purchase #4 $185.55   7.412%   $199.303   $199.30   $199.30   $199.30  
  Purchase #5 $98.90   4.439%   $103.2902   $103.29   $103.30   $103.30  
  Purchase #6 $83.59   13.203%   $94.6264   $94.63   $94.65   $94.60  
  Purchase #7 $216.73   11.813%   $242.3323   $242.33   $242.35   $242.30  
  7 purchase totals = $946.88       $1,015.6242   $1,015.62   $1,015.70   $1,015.50