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	$6.75	11.735%	$7.5421	$7.54	$7.55	$7.50
Purchase #2	$167.65	5.254%	$176.4583	$176.46	$176.45	$176.50
Purchase #3	$44.25	11.223%	$49.2162	$49.22	$49.20	$49.20
Purchase #4	$27.25	6.823%	$29.1093	$29.11	$29.10	$29.10
Purchase #5	$48.44	10.648%	$53.5979	$53.60	$53.60	$53.60
Purchase #6	$66.91	6.532%	$71.2806	$71.28	$71.30	$71.30
Purchase #7	$230.47	10.281%	$254.1646	$254.16	$254.15	$254.20
7 purchase totals =	$591.72		$641.3690	$641.37	$641.35	$641.40