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	$95.87	10.619%	$106.0504	$106.05	$106.05	$106.10
Purchase #2	$17.96	12.379%	$20.1833	$20.18	$20.20	$20.20
Purchase #3	$122.92	11.791%	$137.4135	$137.41	$137.40	$137.40
Purchase #4	$94.51	11.455%	$105.3361	$105.34	$105.35	$105.30
Purchase #5	$128.48	6.305%	$136.5807	$136.58	$136.60	$136.60
Purchase #6	$41.72	9.644%	$45.7435	$45.74	$45.75	$45.70
Purchase #7	$76.26	3.321%	$78.7926	$78.79	$78.80	$78.80
7 purchase totals =	$577.72		$630.1001	$630.09	$630.15	$630.10