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	$134.84	6.733%	$143.9188	$143.92	$143.90	$143.90
Purchase #2	$153.44	11.638%	$171.2973	$171.30	$171.30	$171.30
Purchase #3	$97.72	6.243%	$103.8207	$103.82	$103.80	$103.80
Purchase #4	$181.90	8.575%	$197.4979	$197.50	$197.50	$197.50
Purchase #5	$146.39	7.119%	$156.8115	$156.81	$156.80	$156.80
Purchase #6	$95.86	9.699%	$105.1575	$105.16	$105.15	$105.20
Purchase #7	$218.49	10.761%	$242.0017	$242.00	$242.00	$242.00
7 purchase totals =	$1,028.64		$1,120.5054	$1,120.51	$1,120.45	$1,120.50