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 $243.98   7.627%   $262.5884   $262.59   $262.60   $262.60  
  Purchase #2 $46.88   13.800%   $53.3494   $53.35   $53.35   $53.30  
  Purchase #3 $89.25   7.803%   $96.2142   $96.21   $96.20   $96.20  
  Purchase #4 $203.67   8.779%   $221.5502   $221.55   $221.55   $221.60  
  Purchase #5 $54.76   13.678%   $62.2501   $62.25   $62.25   $62.30  
  Purchase #6 $42.73   3.553%   $44.2482   $44.25   $44.25   $44.20  
  Purchase #7 $176.27   13.177%   $199.4971   $199.50   $199.50   $199.50  
  7 purchase totals = $857.54       $939.6976   $939.70   $939.70   $939.70