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	$145.72	13.719%	$165.7113	$165.71	$165.70	$165.70
Purchase #2	$189.34	10.694%	$209.588	$209.59	$209.60	$209.60
Purchase #3	$78.46	3.434%	$81.1543	$81.15	$81.15	$81.20
Purchase #4	$11.43	10.788%	$12.6631	$12.66	$12.65	$12.70
Purchase #5	$37.29	3.790%	$38.7033	$38.70	$38.70	$38.70
Purchase #6	$224.38	11.320%	$249.7798	$249.78	$249.80	$249.80
Purchase #7	$55.27	4.166%	$57.5725	$57.57	$57.55	$57.60
7 purchase totals =	$741.89		$815.1723	$815.16	$815.15	$815.30