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	$134.51	13.366%	$152.4886	$152.49	$152.50	$152.50
Purchase #2	$49.50	10.824%	$54.8579	$54.86	$54.85	$54.90
Purchase #3	$111.87	5.403%	$117.9143	$117.91	$117.90	$117.90
Purchase #4	$119.60	5.486%	$126.1613	$126.16	$126.15	$126.20
Purchase #5	$23.72	7.611%	$25.5253	$25.53	$25.55	$25.50
Purchase #6	$224.67	8.113%	$242.8975	$242.90	$242.90	$242.90
Purchase #7	$167.92	6.863%	$179.4443	$179.44	$179.45	$179.40
7 purchase totals =	$831.79		$899.2892	$899.29	$899.30	$899.30