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	$83.90	5.699%	$88.6815	$88.68	$88.70	$88.70
Purchase #2	$78.33	5.745%	$82.8301	$82.83	$82.85	$82.80
Purchase #3	$29.31	10.501%	$32.3878	$32.39	$32.40	$32.40
Purchase #4	$99.40	6.862%	$106.2208	$106.22	$106.20	$106.20
Purchase #5	$61.27	9.137%	$66.8682	$66.87	$66.85	$66.90
Purchase #6	$54.90	10.647%	$60.7452	$60.75	$60.75	$60.70
Purchase #7	$18.30	10.746%	$20.2665	$20.27	$20.25	$20.30
7 purchase totals =	$425.41		$458.0001	$458.01	$458.00	$458.00