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	$162.82	5.819%	$172.2945	$172.29	$172.30	$172.30
Purchase #2	$18.39	10.472%	$20.3158	$20.32	$20.30	$20.30
Purchase #3	$122.64	10.153%	$135.0916	$135.09	$135.10	$135.10
Purchase #4	$51.54	13.470%	$58.4824	$58.48	$58.50	$58.50
Purchase #5	$86.33	4.747%	$90.4281	$90.43	$90.45	$90.40
Purchase #6	$87.41	3.671%	$90.6188	$90.62	$90.60	$90.60
Purchase #7	$16.78	9.486%	$18.3718	$18.37	$18.35	$18.40
7 purchase totals =	$545.91		$585.6030	$585.60	$585.60	$585.60