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	$43.88	4.309%	$45.7708	$45.77	$45.75	$45.80
Purchase #2	$240.32	7.478%	$258.2911	$258.29	$258.30	$258.30
Purchase #3	$48.71	12.817%	$54.9532	$54.95	$54.95	$55.00
Purchase #4	$11.58	9.464%	$12.6759	$12.68	$12.70	$12.70
Purchase #5	$18.54	13.110%	$20.9706	$20.97	$20.95	$21.00
Purchase #6	$71.91	9.404%	$78.6724	$78.67	$78.65	$78.70
Purchase #7	$159.62	9.742%	$175.1702	$175.17	$175.15	$175.20
7 purchase totals =	$594.56		$646.5042	$646.50	$646.45	$646.70