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 $221.59   12.235%   $248.7015   $248.70   $248.70   $248.70  
  Purchase #2 $72.60   12.452%   $81.6402   $81.64   $81.65   $81.60  
  Purchase #3 $54.88   4.822%   $57.5263   $57.53   $57.55   $57.50  
  Purchase #4 $94.39   9.572%   $103.425   $103.43   $103.45   $103.40  
  Purchase #5 $201.68   11.137%   $224.1411   $224.14   $224.15   $224.10  
  Purchase #6 $36.92   9.734%   $40.5138   $40.51   $40.50   $40.50  
  Purchase #7 $185.38   7.871%   $199.9713   $199.97   $199.95   $200.00  
  7 purchase totals = $867.44       $955.9192   $955.92   $955.95   $955.80