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	$158.52	13.292%	$179.5905	$179.59	$179.60	$179.60
Purchase #2	$51.29	6.819%	$54.7875	$54.79	$54.80	$54.80
Purchase #3	$235.83	9.827%	$259.005	$259.01	$259.00	$259.00
Purchase #4	$73.72	5.186%	$77.5431	$77.54	$77.55	$77.50
Purchase #5	$68.87	3.151%	$71.0401	$71.04	$71.05	$71.00
Purchase #6	$117.92	10.797%	$130.6518	$130.65	$130.65	$130.70
Purchase #7	$151.45	9.382%	$165.659	$165.66	$165.65	$165.70
7 purchase totals =	$857.60		$938.2770	$938.28	$938.30	$938.30