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	$34.52	10.714%	$38.2185	$38.22	$38.20	$38.20
Purchase #2	$88.51	13.237%	$100.2261	$100.23	$100.25	$100.20
Purchase #3	$146.77	10.675%	$162.4377	$162.44	$162.45	$162.40
Purchase #4	$128.44	13.496%	$145.7743	$145.77	$145.75	$145.80
Purchase #5	$245.31	11.337%	$273.1208	$273.12	$273.10	$273.10
Purchase #6	$62.81	13.407%	$71.2309	$71.23	$71.25	$71.20
Purchase #7	$69.32	8.410%	$75.1498	$75.15	$75.15	$75.10
7 purchase totals =	$775.68		$866.1581	$866.16	$866.15	$866.00