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	$145.28	9.591%	$159.2138	$159.21	$159.20	$159.20
Purchase #2	$129.62	8.653%	$140.836	$140.84	$140.85	$140.80
Purchase #3	$56.81	6.555%	$60.5339	$60.53	$60.55	$60.50
Purchase #4	$85.58	4.141%	$89.1239	$89.12	$89.10	$89.10
Purchase #5	$215.56	11.685%	$240.7482	$240.75	$240.75	$240.70
Purchase #6	$128.40	13.779%	$146.0922	$146.09	$146.10	$146.10
Purchase #7	$35.60	6.528%	$37.924	$37.92	$37.90	$37.90
7 purchase totals =	$796.85		$874.4720	$874.46	$874.45	$874.30