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	$152.55	11.798%	$170.5478	$170.55	$170.55	$170.50
Purchase #2	$166.83	3.436%	$172.5623	$172.56	$172.55	$172.60
Purchase #3	$37.85	5.547%	$39.9495	$39.95	$39.95	$39.90
Purchase #4	$123.60	13.156%	$139.8608	$139.86	$139.85	$139.90
Purchase #5	$134.39	9.301%	$146.8896	$146.89	$146.90	$146.90
Purchase #6	$156.73	3.830%	$162.7328	$162.73	$162.75	$162.70
Purchase #7	$126.86	9.736%	$139.2111	$139.21	$139.20	$139.20
7 purchase totals =	$898.81		$971.7539	$971.75	$971.75	$971.70