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	$122.58	3.725%	$127.1461	$127.15	$127.15	$127.10
Purchase #2	$242.72	8.222%	$262.6764	$262.68	$262.70	$262.70
Purchase #3	$52.56	9.628%	$57.6205	$57.62	$57.60	$57.60
Purchase #4	$87.28	8.685%	$94.8603	$94.86	$94.85	$94.90
Purchase #5	$77.39	12.135%	$86.7813	$86.78	$86.80	$86.80
Purchase #6	$123.37	12.808%	$139.1712	$139.17	$139.15	$139.20
Purchase #7	$145.33	6.205%	$154.3477	$154.35	$154.35	$154.30
7 purchase totals =	$851.23		$922.6035	$922.61	$922.60	$922.60