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 $242.97   10.322%   $268.0494   $268.05   $268.05   $268.00  
  Purchase #2 $230.38   11.534%   $256.952   $256.95   $256.95   $257.00  
  Purchase #3 $119.90   9.430%   $131.2066   $131.21   $131.20   $131.20  
  Purchase #4 $32.61   9.665%   $35.7618   $35.76   $35.75   $35.80  
  Purchase #5 $137.35   3.869%   $142.6641   $142.66   $142.65   $142.70  
  Purchase #6 $166.50   11.501%   $185.6492   $185.65   $185.65   $185.60  
  Purchase #7 $183.68   11.468%   $204.7444   $204.74   $204.75   $204.70  
  7 purchase totals = $1,113.39       $1,225.0275   $1,225.02   $1,225.00   $1,225.00