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	$165.68	7.681%	$178.4059	$178.41	$178.40	$178.40
Purchase #2	$227.33	13.325%	$257.6217	$257.62	$257.60	$257.60
Purchase #3	$21.89	12.588%	$24.6455	$24.65	$24.65	$24.60
Purchase #4	$87.43	6.693%	$93.2817	$93.28	$93.30	$93.30
Purchase #5	$138.83	5.387%	$146.3088	$146.31	$146.30	$146.30
Purchase #6	$62.40	10.577%	$69	$69.00	$69.00	$69.00
Purchase #7	$56.94	4.123%	$59.2876	$59.29	$59.30	$59.30
7 purchase totals =	$760.50		$828.5512	$828.56	$828.55	$828.50