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	$238.26	6.539%	$253.8398	$253.84	$253.85	$253.80
Purchase #2	$35.90	7.841%	$38.7149	$38.71	$38.70	$38.70
Purchase #3	$157.60	3.141%	$162.5502	$162.55	$162.55	$162.60
Purchase #4	$100.68	10.440%	$111.191	$111.19	$111.20	$111.20
Purchase #5	$214.86	9.663%	$235.6219	$235.62	$235.60	$235.60
Purchase #6	$87.88	13.535%	$99.7746	$99.77	$99.75	$99.80
Purchase #7	$53.86	7.496%	$57.8973	$57.90	$57.90	$57.90
7 purchase totals =	$889.04		$959.5897	$959.58	$959.55	$959.60