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	$142.83	11.477%	$159.2226	$159.22	$159.20	$159.20
Purchase #2	$222.28	5.848%	$235.2789	$235.28	$235.30	$235.30
Purchase #3	$237.88	5.694%	$251.4249	$251.42	$251.40	$251.40
Purchase #4	$100.47	10.791%	$111.3117	$111.31	$111.30	$111.30
Purchase #5	$95.42	13.515%	$108.316	$108.32	$108.30	$108.30
Purchase #6	$231.94	12.481%	$260.8884	$260.89	$260.90	$260.90
Purchase #7	$103.31	8.405%	$111.9932	$111.99	$112.00	$112.00
7 purchase totals =	$1,134.13		$1,238.4357	$1,238.43	$1,238.40	$1,238.40