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	$225.62	11.429%	$251.4061	$251.41	$251.40	$251.40
Purchase #2	$54.25	13.862%	$61.7701	$61.77	$61.75	$61.80
Purchase #3	$109.46	9.508%	$119.8675	$119.87	$119.85	$119.90
Purchase #4	$126.76	5.840%	$134.1628	$134.16	$134.15	$134.20
Purchase #5	$48.38	11.560%	$53.9727	$53.97	$53.95	$54.00
Purchase #6	$10.37	7.301%	$11.1271	$11.13	$11.15	$11.10
Purchase #7	$88.43	4.563%	$92.4651	$92.47	$92.45	$92.50
7 purchase totals =	$663.27		$724.7714	$724.78	$724.70	$724.90