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	$95.93	3.635%	$99.4171	$99.42	$99.40	$99.40
Purchase #2	$45.48	6.868%	$48.6036	$48.60	$48.60	$48.60
Purchase #3	$186.48	6.819%	$199.1961	$199.20	$199.20	$199.20
Purchase #4	$228.33	11.801%	$255.2752	$255.28	$255.30	$255.30
Purchase #5	$127.62	7.574%	$137.2859	$137.29	$137.30	$137.30
Purchase #6	$90.28	6.854%	$96.4678	$96.47	$96.45	$96.50
Purchase #7	$20.97	10.514%	$23.1748	$23.17	$23.15	$23.20
7 purchase totals =	$795.09		$859.4205	$859.43	$859.40	$859.50