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	$241.34	12.238%	$270.8752	$270.88	$270.90	$270.90
Purchase #2	$130.94	9.346%	$143.1777	$143.18	$143.20	$143.20
Purchase #3	$38.57	5.292%	$40.6111	$40.61	$40.60	$40.60
Purchase #4	$210.37	8.722%	$228.7185	$228.72	$228.70	$228.70
Purchase #5	$67.39	7.147%	$72.2064	$72.21	$72.20	$72.20
Purchase #6	$226.27	12.513%	$254.5832	$254.58	$254.60	$254.60
Purchase #7	$167.45	10.434%	$184.9217	$184.92	$184.90	$184.90
7 purchase totals =	$1,082.33		$1,195.0938	$1,195.10	$1,195.10	$1,195.10