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	$35.40	8.585%	$38.4391	$38.44	$38.45	$38.40
Purchase #2	$34.35	11.854%	$38.4218	$38.42	$38.40	$38.40
Purchase #3	$72.49	13.536%	$82.3022	$82.30	$82.30	$82.30
Purchase #4	$17.95	13.847%	$20.4355	$20.44	$20.45	$20.40
Purchase #5	$250.97	9.634%	$275.1484	$275.15	$275.15	$275.10
Purchase #6	$137.92	9.512%	$151.039	$151.04	$151.05	$151.00
Purchase #7	$34.50	5.869%	$36.5248	$36.52	$36.50	$36.50
7 purchase totals =	$583.58		$642.3108	$642.31	$642.30	$642.10