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	$175.69	12.468%	$197.595	$197.60	$197.60	$197.60
Purchase #2	$245.72	13.852%	$279.7571	$279.76	$279.75	$279.80
Purchase #3	$47.30	10.553%	$52.2916	$52.29	$52.30	$52.30
Purchase #4	$52.43	4.109%	$54.5843	$54.58	$54.60	$54.60
Purchase #5	$120.29	8.647%	$130.6915	$130.69	$130.70	$130.70
Purchase #6	$87.50	5.804%	$92.5785	$92.58	$92.60	$92.60
Purchase #7	$170.86	11.664%	$190.7891	$190.79	$190.80	$190.80
7 purchase totals =	$899.79		$998.2871	$998.29	$998.35	$998.40