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	$9.42	11.683%	$10.5205	$10.52	$10.50	$10.50
Purchase #2	$74.30	12.231%	$83.3876	$83.39	$83.40	$83.40
Purchase #3	$94.43	6.354%	$100.4301	$100.43	$100.45	$100.40
Purchase #4	$70.51	10.177%	$77.6858	$77.69	$77.70	$77.70
Purchase #5	$229.83	7.677%	$247.474	$247.47	$247.45	$247.50
Purchase #6	$9.33	7.446%	$10.0247	$10.02	$10.00	$10.00
Purchase #7	$26.56	12.173%	$29.7931	$29.79	$29.80	$29.80
7 purchase totals =	$514.38		$559.3158	$559.31	$559.30	$559.30