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 $55.88   12.126%   $62.656   $62.66   $62.65   $62.70  
  Purchase #2 $17.39   5.596%   $18.3631   $18.36   $18.35   $18.40  
  Purchase #3 $44.76   4.328%   $46.6972   $46.70   $46.70   $46.70  
  Purchase #4 $215.73   4.149%   $224.6806   $224.68   $224.70   $224.70  
  Purchase #5 $173.29   7.841%   $186.8777   $186.88   $186.90   $186.90  
  Purchase #6 $119.96   8.152%   $129.7391   $129.74   $129.75   $129.70  
  Purchase #7 $153.67   3.743%   $159.4219   $159.42   $159.40   $159.40  
  7 purchase totals = $780.68       $828.4356   $828.44   $828.45   $828.50