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	$135.57	8.716%	$147.3863	$147.39	$147.40	$147.40
Purchase #2	$231.49	10.346%	$255.44	$255.44	$255.45	$255.40
Purchase #3	$237.26	8.698%	$257.8969	$257.90	$257.90	$257.90
Purchase #4	$139.42	10.398%	$153.9169	$153.92	$153.90	$153.90
Purchase #5	$205.58	10.840%	$227.8649	$227.86	$227.85	$227.90
Purchase #6	$118.36	7.411%	$127.1317	$127.13	$127.15	$127.10
Purchase #7	$29.49	5.854%	$31.2163	$31.22	$31.20	$31.20
7 purchase totals =	$1,097.17		$1,200.8530	$1,200.86	$1,200.85	$1,200.80