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	$234.85	13.317%	$266.125	$266.13	$266.15	$266.10
Purchase #2	$87.96	3.104%	$90.6903	$90.69	$90.70	$90.70
Purchase #3	$52.90	13.176%	$59.8701	$59.87	$59.85	$59.90
Purchase #4	$175.72	9.428%	$192.2869	$192.29	$192.30	$192.30
Purchase #5	$231.46	6.353%	$246.1647	$246.16	$246.15	$246.20
Purchase #6	$184.78	8.702%	$200.8596	$200.86	$200.85	$200.90
Purchase #7	$163.78	8.177%	$177.1723	$177.17	$177.15	$177.20
7 purchase totals =	$1,131.45		$1,233.1689	$1,233.17	$1,233.15	$1,233.30