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	$107.36	12.499%	$120.7789	$120.78	$120.80	$120.80
Purchase #2	$232.71	9.649%	$255.1642	$255.16	$255.15	$255.20
Purchase #3	$119.78	6.336%	$127.3693	$127.37	$127.35	$127.40
Purchase #4	$181.91	13.160%	$205.8494	$205.85	$205.85	$205.80
Purchase #5	$179.68	4.117%	$187.0774	$187.08	$187.10	$187.10
Purchase #6	$132.93	6.484%	$141.5492	$141.55	$141.55	$141.50
Purchase #7	$124.26	5.266%	$130.8035	$130.80	$130.80	$130.80
7 purchase totals =	$1,078.63		$1,168.5919	$1,168.59	$1,168.60	$1,168.60