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	$234.72	5.610%	$247.8878	$247.89	$247.90	$247.90
Purchase #2	$88.91	7.516%	$95.5925	$95.59	$95.60	$95.60
Purchase #3	$181.54	3.294%	$187.5199	$187.52	$187.50	$187.50
Purchase #4	$149.79	8.286%	$162.2016	$162.20	$162.20	$162.20
Purchase #5	$130.47	5.559%	$137.7228	$137.72	$137.70	$137.70
Purchase #6	$81.73	11.718%	$91.3071	$91.31	$91.30	$91.30
Purchase #7	$49.45	10.412%	$54.5987	$54.60	$54.60	$54.60
7 purchase totals =	$916.61		$976.8304	$976.83	$976.80	$976.80