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	$245.55	8.663%	$266.822	$266.82	$266.80	$266.80
Purchase #2	$166.68	10.729%	$184.5631	$184.56	$184.55	$184.60
Purchase #3	$19.81	4.786%	$20.7581	$20.76	$20.75	$20.80
Purchase #4	$129.31	11.806%	$144.5763	$144.58	$144.60	$144.60
Purchase #5	$86.87	4.690%	$90.9442	$90.94	$90.95	$90.90
Purchase #6	$185.83	3.651%	$192.6147	$192.61	$192.60	$192.60
Purchase #7	$247.73	6.497%	$263.825	$263.83	$263.85	$263.80
7 purchase totals =	$1,081.78		$1,164.1034	$1,164.10	$1,164.10	$1,164.10