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	$149.70	10.597%	$165.5637	$165.56	$165.55	$165.60
Purchase #2	$209.92	4.733%	$219.8555	$219.86	$219.85	$219.90
Purchase #3	$14.31	12.368%	$16.0799	$16.08	$16.10	$16.10
Purchase #4	$130.78	8.698%	$142.1552	$142.16	$142.15	$142.20
Purchase #5	$10.71	3.791%	$11.116	$11.12	$11.10	$11.10
Purchase #6	$48.31	4.257%	$50.3666	$50.37	$50.35	$50.40
Purchase #7	$57.58	7.297%	$61.7816	$61.78	$61.80	$61.80
7 purchase totals =	$621.31		$666.9185	$666.93	$666.90	$667.10