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	$59.32	12.388%	$66.6686	$66.67	$66.65	$66.70
Purchase #2	$153.28	4.145%	$159.6335	$159.63	$159.65	$159.60
Purchase #3	$104.93	8.278%	$113.6161	$113.62	$113.60	$113.60
Purchase #4	$237.44	8.857%	$258.4701	$258.47	$258.45	$258.50
Purchase #5	$158.96	5.842%	$168.2464	$168.25	$168.25	$168.20
Purchase #6	$25.98	11.246%	$28.9017	$28.90	$28.90	$28.90
Purchase #7	$227.37	12.205%	$255.1205	$255.12	$255.10	$255.10
7 purchase totals =	$967.28		$1,050.6569	$1,050.66	$1,050.60	$1,050.60