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 $240.41   10.411%   $265.4391   $265.44   $265.45   $265.40  
  Purchase #2 $180.63   8.476%   $195.9402   $195.94   $195.95   $195.90  
  Purchase #3 $55.67   4.185%   $57.9998   $58.00   $58.00   $58.00  
  Purchase #4 $249.73   10.629%   $276.2738   $276.27   $276.25   $276.30  
  Purchase #5 $192.80   6.412%   $205.1623   $205.16   $205.15   $205.20  
  Purchase #6 $42.47   6.375%   $45.1775   $45.18   $45.20   $45.20  
  Purchase #7 $69.29   10.477%   $76.5495   $76.55   $76.55   $76.50  
  7 purchase totals = $1,031.00       $1,122.5422   $1,122.54   $1,122.55   $1,122.50