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	$51.87	5.627%	$54.7887	$54.79	$54.80	$54.80
Purchase #2	$137.79	10.274%	$151.9465	$151.95	$151.95	$151.90
Purchase #3	$145.41	13.673%	$165.2919	$165.29	$165.30	$165.30
Purchase #4	$217.27	3.240%	$224.3095	$224.31	$224.30	$224.30
Purchase #5	$34.66	8.276%	$37.5285	$37.53	$37.55	$37.50
Purchase #6	$44.55	12.794%	$50.2497	$50.25	$50.25	$50.20
Purchase #7	$235.31	12.552%	$264.8461	$264.85	$264.85	$264.80
7 purchase totals =	$866.86		$948.9609	$948.97	$949.00	$948.80