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	$145.89	7.414%	$156.7063	$156.71	$156.70	$156.70
Purchase #2	$149.54	10.690%	$165.5258	$165.53	$165.55	$165.50
Purchase #3	$88.45	10.849%	$98.0459	$98.05	$98.05	$98.00
Purchase #4	$90.57	12.300%	$101.7101	$101.71	$101.70	$101.70
Purchase #5	$9.91	10.205%	$10.9213	$10.92	$10.90	$10.90
Purchase #6	$166.49	5.468%	$175.5937	$175.59	$175.60	$175.60
Purchase #7	$67.30	8.594%	$73.0838	$73.08	$73.10	$73.10
7 purchase totals =	$718.15		$781.5869	$781.59	$781.60	$781.50