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	$74.81	6.197%	$79.446	$79.45	$79.45	$79.40
Purchase #2	$224.69	11.847%	$251.309	$251.31	$251.30	$251.30
Purchase #3	$189.76	10.231%	$209.1743	$209.17	$209.15	$209.20
Purchase #4	$237.83	10.103%	$261.858	$261.86	$261.85	$261.90
Purchase #5	$169.32	11.163%	$188.2212	$188.22	$188.20	$188.20
Purchase #6	$112.25	13.456%	$127.3544	$127.35	$127.35	$127.40
Purchase #7	$132.27	4.200%	$137.8253	$137.83	$137.85	$137.80
7 purchase totals =	$1,140.93		$1,255.1882	$1,255.19	$1,255.15	$1,255.20