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 $109.63   8.858%   $119.341   $119.34   $119.35   $119.30  
  Purchase #2 $19.26   13.845%   $21.9265   $21.93   $21.95   $21.90  
  Purchase #3 $76.63   13.508%   $86.9812   $86.98   $87.00   $87.00  
  Purchase #4 $116.54   3.386%   $120.486   $120.49   $120.50   $120.50  
  Purchase #5 $229.34   6.395%   $244.0063   $244.01   $244.00   $244.00  
  Purchase #6 $34.98   10.401%   $38.6183   $38.62   $38.60   $38.60  
  Purchase #7 $175.59   12.178%   $196.9734   $196.97   $196.95   $197.00  
  7 purchase totals = $761.97       $828.3327   $828.34   $828.35   $828.30