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 $248.41   6.784%   $265.2621   $265.26   $265.25   $265.30  
  Purchase #2 $206.68   7.615%   $222.4187   $222.42   $222.40   $222.40  
  Purchase #3 $83.39   4.643%   $87.2618   $87.26   $87.25   $87.30  
  Purchase #4 $206.48   5.203%   $217.2232   $217.22   $217.20   $217.20  
  Purchase #5 $6.51   5.305%   $6.8554   $6.86   $6.85   $6.90  
  Purchase #6 $90.91   3.804%   $94.3682   $94.37   $94.35   $94.40  
  Purchase #7 $55.39   10.728%   $61.3322   $61.33   $61.35   $61.30  
  7 purchase totals = $897.77       $954.7216   $954.72   $954.65   $954.80