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	$73.47	11.510%	$81.9264	$81.93	$81.95	$81.90
Purchase #2	$98.84	9.684%	$108.4117	$108.41	$108.40	$108.40
Purchase #3	$109.35	12.830%	$123.3796	$123.38	$123.40	$123.40
Purchase #4	$220.41	7.660%	$237.2934	$237.29	$237.30	$237.30
Purchase #5	$187.66	11.741%	$209.6932	$209.69	$209.70	$209.70
Purchase #6	$150.30	6.762%	$160.4633	$160.46	$160.45	$160.50
Purchase #7	$64.61	11.460%	$72.0143	$72.01	$72.00	$72.00
7 purchase totals =	$904.64		$993.1819	$993.17	$993.20	$993.20