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	$156.46	5.750%	$165.4565	$165.46	$165.45	$165.50
Purchase #2	$224.40	11.494%	$250.1925	$250.19	$250.20	$250.20
Purchase #3	$46.53	12.785%	$52.4789	$52.48	$52.50	$52.50
Purchase #4	$32.75	13.846%	$37.2846	$37.28	$37.30	$37.30
Purchase #5	$151.39	11.525%	$168.8377	$168.84	$168.85	$168.80
Purchase #6	$114.50	13.619%	$130.0938	$130.09	$130.10	$130.10
Purchase #7	$112.37	8.734%	$122.1844	$122.18	$122.20	$122.20
7 purchase totals =	$838.40		$926.5284	$926.52	$926.60	$926.60