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	$129.34	6.383%	$137.5958	$137.60	$137.60	$137.60
Purchase #2	$44.83	12.108%	$50.258	$50.26	$50.25	$50.30
Purchase #3	$141.39	3.612%	$146.497	$146.50	$146.50	$146.50
Purchase #4	$231.51	5.718%	$244.7477	$244.75	$244.75	$244.70
Purchase #5	$127.70	10.174%	$140.6922	$140.69	$140.70	$140.70
Purchase #6	$74.32	4.221%	$77.457	$77.46	$77.45	$77.50
Purchase #7	$182.49	4.240%	$190.2276	$190.23	$190.25	$190.20
7 purchase totals =	$931.58		$987.4753	$987.49	$987.50	$987.50