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	$18.54	12.659%	$20.887	$20.89	$20.90	$20.90
Purchase #2	$85.51	5.440%	$90.1617	$90.16	$90.15	$90.20
Purchase #3	$64.77	7.839%	$69.8473	$69.85	$69.85	$69.80
Purchase #4	$227.78	10.863%	$252.5237	$252.52	$252.50	$252.50
Purchase #5	$158.33	9.486%	$173.3492	$173.35	$173.35	$173.30
Purchase #6	$40.28	7.830%	$43.4339	$43.43	$43.45	$43.40
Purchase #7	$22.32	4.142%	$23.2445	$23.24	$23.25	$23.20
7 purchase totals =	$617.53		$673.4473	$673.44	$673.45	$673.30