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	$152.82	5.102%	$160.6169	$160.62	$160.60	$160.60
Purchase #2	$69.52	8.424%	$75.3764	$75.38	$75.40	$75.40
Purchase #3	$59.38	9.817%	$65.2093	$65.21	$65.20	$65.20
Purchase #4	$149.54	3.698%	$155.07	$155.07	$155.05	$155.10
Purchase #5	$46.72	6.366%	$49.6942	$49.69	$49.70	$49.70
Purchase #6	$99.63	12.303%	$111.8875	$111.89	$111.90	$111.90
Purchase #7	$181.72	4.388%	$189.6939	$189.69	$189.70	$189.70
7 purchase totals =	$759.33		$807.5482	$807.55	$807.55	$807.60