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	$88.42	13.493%	$100.3505	$100.35	$100.35	$100.40
Purchase #2	$36.75	11.358%	$40.9241	$40.92	$40.90	$40.90
Purchase #3	$45.40	6.620%	$48.4055	$48.41	$48.40	$48.40
Purchase #4	$31.68	11.653%	$35.3717	$35.37	$35.35	$35.40
Purchase #5	$215.56	6.475%	$229.5175	$229.52	$229.50	$229.50
Purchase #6	$37.48	4.305%	$39.0935	$39.09	$39.10	$39.10
Purchase #7	$140.71	8.680%	$152.9236	$152.92	$152.90	$152.90
7 purchase totals =	$596.00		$646.5864	$646.58	$646.50	$646.60