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	$20.37	10.377%	$22.4838	$22.48	$22.50	$22.50
Purchase #2	$183.30	11.843%	$205.0082	$205.01	$205.00	$205.00
Purchase #3	$127.57	12.741%	$143.8237	$143.82	$143.80	$143.80
Purchase #4	$146.43	10.707%	$162.1083	$162.11	$162.10	$162.10
Purchase #5	$91.34	12.139%	$102.4278	$102.43	$102.45	$102.40
Purchase #6	$238.84	3.519%	$247.2448	$247.24	$247.25	$247.20
Purchase #7	$173.77	6.199%	$184.542	$184.54	$184.55	$184.50
7 purchase totals =	$981.62		$1,067.6386	$1,067.63	$1,067.65	$1,067.50