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	$160.87	4.193%	$167.6153	$167.62	$167.60	$167.60
Purchase #2	$237.94	9.343%	$260.1707	$260.17	$260.15	$260.20
Purchase #3	$48.87	13.639%	$55.5354	$55.54	$55.55	$55.50
Purchase #4	$41.43	3.224%	$42.7657	$42.77	$42.75	$42.80
Purchase #5	$118.31	4.376%	$123.4872	$123.49	$123.50	$123.50
Purchase #6	$90.43	8.298%	$97.9339	$97.93	$97.95	$97.90
Purchase #7	$196.85	13.151%	$222.7377	$222.74	$222.75	$222.70
7 purchase totals =	$894.70		$970.2459	$970.26	$970.25	$970.20