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	$21.73	8.386%	$23.5523	$23.55	$23.55	$23.60
Purchase #2	$77.78	9.639%	$85.2772	$85.28	$85.30	$85.30
Purchase #3	$155.81	13.104%	$176.2273	$176.23	$176.25	$176.20
Purchase #4	$50.25	11.361%	$55.9589	$55.96	$55.95	$56.00
Purchase #5	$144.63	5.205%	$152.158	$152.16	$152.15	$152.20
Purchase #6	$79.52	13.485%	$90.2433	$90.24	$90.25	$90.20
Purchase #7	$49.47	4.533%	$51.7125	$51.71	$51.70	$51.70
7 purchase totals =	$579.19		$635.1295	$635.13	$635.15	$635.20