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	$203.52	7.301%	$218.379	$218.38	$218.40	$218.40
Purchase #2	$127.94	13.414%	$145.1019	$145.10	$145.10	$145.10
Purchase #3	$185.78	10.838%	$205.9148	$205.91	$205.90	$205.90
Purchase #4	$145.31	3.283%	$150.0805	$150.08	$150.10	$150.10
Purchase #5	$83.72	11.453%	$93.3085	$93.31	$93.30	$93.30
Purchase #6	$98.92	5.401%	$104.2627	$104.26	$104.25	$104.30
Purchase #7	$33.40	3.515%	$34.574	$34.57	$34.55	$34.60
7 purchase totals =	$878.59		$951.6214	$951.61	$951.60	$951.70