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	$89.30	12.814%	$100.7429	$100.74	$100.75	$100.70
Purchase #2	$153.63	7.696%	$165.4534	$165.45	$165.45	$165.50
Purchase #3	$40.47	5.606%	$42.7387	$42.74	$42.75	$42.70
Purchase #4	$129.29	5.827%	$136.8237	$136.82	$136.80	$136.80
Purchase #5	$43.63	4.735%	$45.6959	$45.70	$45.70	$45.70
Purchase #6	$74.54	7.734%	$80.3049	$80.30	$80.30	$80.30
Purchase #7	$99.66	12.300%	$111.9182	$111.92	$111.90	$111.90
7 purchase totals =	$630.52		$683.6777	$683.67	$683.65	$683.60