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	$15.46	12.613%	$17.41	$17.41	$17.40	$17.40
Purchase #2	$233.99	13.139%	$264.7339	$264.73	$264.75	$264.70
Purchase #3	$155.64	8.165%	$168.348	$168.35	$168.35	$168.30
Purchase #4	$103.89	7.690%	$111.8791	$111.88	$111.90	$111.90
Purchase #5	$11.49	3.464%	$11.888	$11.89	$11.90	$11.90
Purchase #6	$140.39	3.406%	$145.1717	$145.17	$145.15	$145.20
Purchase #7	$53.48	5.496%	$56.4193	$56.42	$56.40	$56.40
7 purchase totals =	$714.34		$775.8500	$775.85	$775.85	$775.80