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 $216.99   11.822%   $242.6426   $242.64   $242.65   $242.60  
  Purchase #2 $72.77   3.707%   $75.4676   $75.47   $75.45   $75.50  
  Purchase #3 $42.40   9.314%   $46.3491   $46.35   $46.35   $46.30  
  Purchase #4 $231.68   9.365%   $253.3768   $253.38   $253.40   $253.40  
  Purchase #5 $9.55   11.204%   $10.62   $10.62   $10.60   $10.60  
  Purchase #6 $117.35   9.314%   $128.28   $128.28   $128.30   $128.30  
  Purchase #7 $126.38   7.819%   $136.2617   $136.26   $136.25   $136.30  
  7 purchase totals = $817.12       $892.9978   $893.00   $893.00   $893.00