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	$223.61	7.370%	$240.0901	$240.09	$240.10	$240.10
Purchase #2	$13.59	10.302%	$14.99	$14.99	$15.00	$15.00
Purchase #3	$83.77	13.789%	$95.321	$95.32	$95.30	$95.30
Purchase #4	$111.48	5.574%	$117.6939	$117.69	$117.70	$117.70
Purchase #5	$116.34	13.306%	$131.8202	$131.82	$131.80	$131.80
Purchase #6	$152.60	10.573%	$168.7344	$168.73	$168.75	$168.70
Purchase #7	$9.72	11.780%	$10.865	$10.87	$10.85	$10.90
7 purchase totals =	$711.11		$779.5146	$779.51	$779.50	$779.50