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	$117.29	12.649%	$132.126	$132.13	$132.15	$132.10
Purchase #2	$87.38	3.440%	$90.3859	$90.39	$90.40	$90.40
Purchase #3	$41.67	4.222%	$43.4293	$43.43	$43.45	$43.40
Purchase #4	$243.45	11.677%	$271.8777	$271.88	$271.90	$271.90
Purchase #5	$70.45	4.224%	$73.4258	$73.43	$73.45	$73.40
Purchase #6	$91.86	8.515%	$99.6819	$99.68	$99.70	$99.70
Purchase #7	$118.70	8.678%	$129.0008	$129.00	$129.00	$129.00
7 purchase totals =	$770.80		$839.9274	$839.94	$840.05	$839.90