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	$141.96	12.253%	$159.3544	$159.35	$159.35	$159.40
Purchase #2	$81.31	10.332%	$89.7109	$89.71	$89.70	$89.70
Purchase #3	$105.72	8.638%	$114.8521	$114.85	$114.85	$114.90
Purchase #4	$46.84	8.496%	$50.8195	$50.82	$50.80	$50.80
Purchase #5	$129.96	8.222%	$140.6453	$140.65	$140.65	$140.60
Purchase #6	$153.86	10.103%	$169.4045	$169.40	$169.40	$169.40
Purchase #7	$53.72	7.308%	$57.6459	$57.65	$57.65	$57.60
7 purchase totals =	$713.37		$782.4326	$782.43	$782.40	$782.40