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	$144.50	3.856%	$150.0719	$150.07	$150.05	$150.10
Purchase #2	$113.34	13.676%	$128.8404	$128.84	$128.85	$128.80
Purchase #3	$156.52	6.861%	$167.2588	$167.26	$167.25	$167.30
Purchase #4	$60.32	6.537%	$64.2631	$64.26	$64.25	$64.30
Purchase #5	$127.27	12.493%	$143.1698	$143.17	$143.15	$143.20
Purchase #6	$137.87	13.519%	$156.5086	$156.51	$156.50	$156.50
Purchase #7	$18.70	13.132%	$21.1557	$21.16	$21.15	$21.20
7 purchase totals =	$758.52		$831.2683	$831.27	$831.20	$831.40