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	$240.82	4.153%	$250.8213	$250.82	$250.80	$250.80
Purchase #2	$248.95	5.516%	$262.6821	$262.68	$262.70	$262.70
Purchase #3	$152.51	13.823%	$173.5915	$173.59	$173.60	$173.60
Purchase #4	$111.32	12.464%	$125.1949	$125.19	$125.20	$125.20
Purchase #5	$185.56	9.823%	$203.7876	$203.79	$203.80	$203.80
Purchase #6	$18.33	13.810%	$20.8614	$20.86	$20.85	$20.90
Purchase #7	$100.90	6.550%	$107.509	$107.51	$107.50	$107.50
7 purchase totals =	$1,058.39		$1,144.4478	$1,144.44	$1,144.45	$1,144.50