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	$62.44	12.810%	$70.4386	$70.44	$70.45	$70.40
Purchase #2	$193.61	13.348%	$219.4531	$219.45	$219.45	$219.50
Purchase #3	$61.80	6.150%	$65.6007	$65.60	$65.60	$65.60
Purchase #4	$102.98	8.497%	$111.7302	$111.73	$111.75	$111.70
Purchase #5	$182.50	3.549%	$188.9769	$188.98	$189.00	$189.00
Purchase #6	$153.77	3.783%	$159.5871	$159.59	$159.60	$159.60
Purchase #7	$35.78	5.431%	$37.7232	$37.72	$37.70	$37.70
7 purchase totals =	$792.88		$853.5098	$853.51	$853.55	$853.50