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	$10.54	12.561%	$11.8639	$11.86	$11.85	$11.90
Purchase #2	$223.28	12.706%	$251.65	$251.65	$251.65	$251.70
Purchase #3	$10.67	11.700%	$11.9184	$11.92	$11.90	$11.90
Purchase #4	$73.37	11.213%	$81.597	$81.60	$81.60	$81.60
Purchase #5	$45.38	11.862%	$50.763	$50.76	$50.75	$50.80
Purchase #6	$61.73	8.342%	$66.8795	$66.88	$66.90	$66.90
Purchase #7	$130.87	13.404%	$148.4118	$148.41	$148.40	$148.40
7 purchase totals =	$555.84		$623.0836	$623.08	$623.05	$623.20