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	$117.39	5.217%	$123.5142	$123.51	$123.50	$123.50
Purchase #2	$91.45	4.122%	$95.2196	$95.22	$95.20	$95.20
Purchase #3	$61.66	5.277%	$64.9138	$64.91	$64.90	$64.90
Purchase #4	$160.92	11.590%	$179.5706	$179.57	$179.55	$179.60
Purchase #5	$117.88	10.318%	$130.0429	$130.04	$130.05	$130.00
Purchase #6	$90.90	12.436%	$102.2043	$102.20	$102.20	$102.20
Purchase #7	$241.66	6.227%	$256.7082	$256.71	$256.70	$256.70
7 purchase totals =	$881.86		$952.1736	$952.16	$952.10	$952.10