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	$155.65	10.554%	$172.0773	$172.08	$172.10	$172.10
Purchase #2	$244.40	4.588%	$255.6131	$255.61	$255.60	$255.60
Purchase #3	$19.66	12.525%	$22.1224	$22.12	$22.10	$22.10
Purchase #4	$69.38	3.153%	$71.5676	$71.57	$71.55	$71.60
Purchase #5	$97.62	13.213%	$110.5185	$110.52	$110.50	$110.50
Purchase #6	$64.29	12.796%	$72.5165	$72.52	$72.50	$72.50
Purchase #7	$131.43	4.773%	$137.7032	$137.70	$137.70	$137.70
7 purchase totals =	$782.43		$842.1186	$842.12	$842.05	$842.10