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	$247.55	12.685%	$278.9517	$278.95	$278.95	$279.00
Purchase #2	$151.88	13.380%	$172.2015	$172.20	$172.20	$172.20
Purchase #3	$188.39	4.235%	$196.3683	$196.37	$196.35	$196.40
Purchase #4	$152.63	4.554%	$159.5808	$159.58	$159.60	$159.60
Purchase #5	$247.39	12.546%	$278.4275	$278.43	$278.45	$278.40
Purchase #6	$87.77	6.787%	$93.7269	$93.73	$93.75	$93.70
Purchase #7	$47.69	5.177%	$50.1589	$50.16	$50.15	$50.20
7 purchase totals =	$1,123.30		$1,229.4156	$1,229.42	$1,229.45	$1,229.50