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 $244.34   9.859%   $268.4295   $268.43   $268.45   $268.40  
  Purchase #2 $85.39   12.760%   $96.2858   $96.29   $96.30   $96.30  
  Purchase #3 $143.45   7.333%   $153.9692   $153.97   $153.95   $154.00  
  Purchase #4 $239.42   8.687%   $260.2184   $260.22   $260.20   $260.20  
  Purchase #5 $191.71   12.425%   $215.53   $215.53   $215.55   $215.50  
  Purchase #6 $235.48   8.514%   $255.5288   $255.53   $255.55   $255.50  
  Purchase #7 $165.68   6.253%   $176.04   $176.04   $176.05   $176.00  
  7 purchase totals = $1,305.47       $1,426.0017   $1,426.01   $1,426.05   $1,425.90