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	$59.30	12.829%	$66.9076	$66.91	$66.90	$66.90
Purchase #2	$210.68	13.386%	$238.8816	$238.88	$238.90	$238.90
Purchase #3	$129.40	11.627%	$144.4453	$144.45	$144.45	$144.40
Purchase #4	$186.29	4.713%	$195.0698	$195.07	$195.05	$195.10
Purchase #5	$202.80	3.102%	$209.0909	$209.09	$209.10	$209.10
Purchase #6	$107.55	3.268%	$111.0647	$111.06	$111.05	$111.10
Purchase #7	$153.26	8.261%	$165.9208	$165.92	$165.90	$165.90
7 purchase totals =	$1,049.28		$1,131.3807	$1,131.38	$1,131.35	$1,131.40