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	$17.42	4.195%	$18.1508	$18.15	$18.15	$18.20
Purchase #2	$123.89	5.117%	$130.2295	$130.23	$130.25	$130.20
Purchase #3	$124.39	10.803%	$137.8279	$137.83	$137.85	$137.80
Purchase #4	$147.48	4.673%	$154.3717	$154.37	$154.35	$154.40
Purchase #5	$48.80	6.424%	$51.9349	$51.93	$51.95	$51.90
Purchase #6	$196.30	9.336%	$214.6266	$214.63	$214.65	$214.60
Purchase #7	$128.35	8.505%	$139.2662	$139.27	$139.25	$139.30
7 purchase totals =	$786.63		$846.4076	$846.41	$846.45	$846.40