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	$49.55	3.466%	$51.2674	$51.27	$51.25	$51.30
Purchase #2	$95.80	4.518%	$100.1282	$100.13	$100.15	$100.10
Purchase #3	$50.34	9.713%	$55.2295	$55.23	$55.25	$55.20
Purchase #4	$50.55	13.784%	$57.5178	$57.52	$57.50	$57.50
Purchase #5	$139.68	4.589%	$146.0899	$146.09	$146.10	$146.10
Purchase #6	$173.81	9.775%	$190.7999	$190.80	$190.80	$190.80
Purchase #7	$60.34	8.520%	$65.481	$65.48	$65.50	$65.50
7 purchase totals =	$620.07		$666.5137	$666.52	$666.55	$666.50