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	$26.86	12.234%	$30.1461	$30.15	$30.15	$30.10
Purchase #2	$56.85	13.269%	$64.3934	$64.39	$64.40	$64.40
Purchase #3	$5.52	5.607%	$5.8295	$5.83	$5.85	$5.80
Purchase #4	$72.92	7.864%	$78.6544	$78.65	$78.65	$78.70
Purchase #5	$66.51	6.561%	$70.8737	$70.87	$70.85	$70.90
Purchase #6	$100.41	8.414%	$108.8585	$108.86	$108.85	$108.90
Purchase #7	$179.78	3.385%	$185.8656	$185.87	$185.85	$185.90
7 purchase totals =	$508.85		$544.6212	$544.62	$544.60	$544.70