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	$90.34	8.801%	$98.2908	$98.29	$98.30	$98.30
Purchase #2	$146.82	7.116%	$157.2677	$157.27	$157.25	$157.30
Purchase #3	$40.72	13.458%	$46.2001	$46.20	$46.20	$46.20
Purchase #4	$52.67	5.122%	$55.3678	$55.37	$55.35	$55.40
Purchase #5	$127.83	7.569%	$137.5055	$137.51	$137.50	$137.50
Purchase #6	$196.56	4.123%	$204.6642	$204.66	$204.65	$204.70
Purchase #7	$35.58	13.476%	$40.3748	$40.37	$40.35	$40.40
7 purchase totals =	$690.52		$739.6709	$739.67	$739.60	$739.80