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	$112.59	3.540%	$116.5757	$116.58	$116.60	$116.60
Purchase #2	$73.32	10.566%	$81.067	$81.07	$81.05	$81.10
Purchase #3	$130.35	10.219%	$143.6705	$143.67	$143.65	$143.70
Purchase #4	$18.85	11.463%	$21.0108	$21.01	$21.00	$21.00
Purchase #5	$147.43	8.221%	$159.5502	$159.55	$159.55	$159.60
Purchase #6	$56.69	4.362%	$59.1628	$59.16	$59.15	$59.20
Purchase #7	$175.56	10.338%	$193.7094	$193.71	$193.70	$193.70
7 purchase totals =	$714.79		$774.7464	$774.75	$774.70	$774.90