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	$223.97	13.225%	$253.59	$253.59	$253.60	$253.60
Purchase #2	$83.72	6.809%	$89.4205	$89.42	$89.40	$89.40
Purchase #3	$45.48	5.286%	$47.8841	$47.88	$47.90	$47.90
Purchase #4	$214.44	13.185%	$242.7139	$242.71	$242.70	$242.70
Purchase #5	$47.25	4.298%	$49.2808	$49.28	$49.30	$49.30
Purchase #6	$217.42	6.345%	$231.2153	$231.22	$231.20	$231.20
Purchase #7	$56.47	11.182%	$62.7845	$62.78	$62.80	$62.80
7 purchase totals =	$888.75		$976.8891	$976.88	$976.90	$976.90