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	$142.58	13.283%	$161.5189	$161.52	$161.50	$161.50
Purchase #2	$155.85	6.783%	$166.4213	$166.42	$166.40	$166.40
Purchase #3	$29.26	13.268%	$33.1422	$33.14	$33.15	$33.10
Purchase #4	$207.37	11.506%	$231.23	$231.23	$231.25	$231.20
Purchase #5	$123.72	6.606%	$131.8929	$131.89	$131.90	$131.90
Purchase #6	$9.38	7.240%	$10.0591	$10.06	$10.05	$10.10
Purchase #7	$152.74	6.363%	$162.4588	$162.46	$162.45	$162.50
7 purchase totals =	$820.90		$896.7232	$896.72	$896.70	$896.70