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	$167.34	13.460%	$189.864	$189.86	$189.85	$189.90
Purchase #2	$105.51	5.797%	$111.6264	$111.63	$111.65	$111.60
Purchase #3	$133.53	9.600%	$146.3489	$146.35	$146.35	$146.30
Purchase #4	$129.34	7.805%	$139.435	$139.44	$139.45	$139.40
Purchase #5	$137.78	7.117%	$147.5858	$147.59	$147.60	$147.60
Purchase #6	$116.64	7.528%	$125.4207	$125.42	$125.40	$125.40
Purchase #7	$35.63	12.489%	$40.0798	$40.08	$40.10	$40.10
7 purchase totals =	$825.77		$900.3606	$900.37	$900.40	$900.30