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	$78.56	13.597%	$89.2418	$89.24	$89.25	$89.20
Purchase #2	$118.73	3.161%	$122.4831	$122.48	$122.50	$122.50
Purchase #3	$140.26	9.160%	$153.1078	$153.11	$153.10	$153.10
Purchase #4	$120.78	6.649%	$128.8107	$128.81	$128.80	$128.80
Purchase #5	$156.93	12.543%	$176.6137	$176.61	$176.60	$176.60
Purchase #6	$216.65	13.703%	$246.3375	$246.34	$246.35	$246.30
Purchase #7	$175.84	4.796%	$184.2733	$184.27	$184.25	$184.30
7 purchase totals =	$1,007.75		$1,100.8679	$1,100.86	$1,100.85	$1,100.80