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	$158.68	13.168%	$179.575	$179.58	$179.60	$179.60
Purchase #2	$100.35	10.729%	$111.1166	$111.12	$111.10	$111.10
Purchase #3	$184.47	12.518%	$207.562	$207.56	$207.55	$207.60
Purchase #4	$92.77	13.739%	$105.5157	$105.52	$105.50	$105.50
Purchase #5	$65.95	8.612%	$71.6296	$71.63	$71.65	$71.60
Purchase #6	$19.88	7.723%	$21.4153	$21.42	$21.40	$21.40
Purchase #7	$39.68	10.119%	$43.6952	$43.70	$43.70	$43.70
7 purchase totals =	$661.78		$740.5094	$740.53	$740.50	$740.50