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	$83.75	9.634%	$91.8185	$91.82	$91.80	$91.80
Purchase #2	$99.38	5.772%	$105.1162	$105.12	$105.10	$105.10
Purchase #3	$175.70	11.361%	$195.6613	$195.66	$195.65	$195.70
Purchase #4	$137.92	8.387%	$149.4874	$149.49	$149.50	$149.50
Purchase #5	$42.42	5.422%	$44.72	$44.72	$44.70	$44.70
Purchase #6	$161.34	6.761%	$172.2482	$172.25	$172.25	$172.20
Purchase #7	$238.83	4.376%	$249.2812	$249.28	$249.30	$249.30
7 purchase totals =	$939.34		$1,008.3328	$1,008.34	$1,008.30	$1,008.30