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 $182.86   6.792%   $195.2799   $195.28   $195.30   $195.30  
  Purchase #2 $89.30   10.129%   $98.3452   $98.35   $98.35   $98.30  
  Purchase #3 $235.61   11.516%   $262.7428   $262.74   $262.75   $262.70  
  Purchase #4 $163.46   13.776%   $185.9782   $185.98   $186.00   $186.00  
  Purchase #5 $9.38   9.181%   $10.2412   $10.24   $10.25   $10.20  
  Purchase #6 $55.29   3.458%   $57.2019   $57.20   $57.20   $57.20  
  Purchase #7 $35.90   7.194%   $38.4826   $38.48   $38.50   $38.50  
  7 purchase totals = $771.80       $848.2718   $848.27   $848.35   $848.20