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	$16.37	4.867%	$17.1667	$17.17	$17.15	$17.20
Purchase #2	$34.39	8.786%	$37.4115	$37.41	$37.40	$37.40
Purchase #3	$211.89	8.665%	$230.2503	$230.25	$230.25	$230.30
Purchase #4	$18.73	10.719%	$20.7377	$20.74	$20.75	$20.70
Purchase #5	$87.32	3.349%	$90.2443	$90.24	$90.25	$90.20
Purchase #6	$54.72	13.812%	$62.2779	$62.28	$62.30	$62.30
Purchase #7	$147.50	5.569%	$155.7143	$155.71	$155.70	$155.70
7 purchase totals =	$570.92		$613.8027	$613.80	$613.80	$613.80