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	$50.48	12.725%	$56.9036	$56.90	$56.90	$56.90
Purchase #2	$99.91	11.863%	$111.7623	$111.76	$111.75	$111.80
Purchase #3	$9.78	8.614%	$10.6224	$10.62	$10.60	$10.60
Purchase #4	$132.46	7.665%	$142.6131	$142.61	$142.60	$142.60
Purchase #5	$79.45	8.435%	$86.1516	$86.15	$86.15	$86.20
Purchase #6	$127.61	13.205%	$144.4609	$144.46	$144.45	$144.50
Purchase #7	$127.67	8.569%	$138.61	$138.61	$138.60	$138.60
7 purchase totals =	$627.36		$691.1239	$691.11	$691.05	$691.20