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	$167.68	10.258%	$184.8806	$184.88	$184.90	$184.90
Purchase #2	$70.90	13.339%	$80.3574	$80.36	$80.35	$80.40
Purchase #3	$183.52	7.470%	$197.2289	$197.23	$197.25	$197.20
Purchase #4	$229.32	11.638%	$256.0083	$256.01	$256.00	$256.00
Purchase #5	$173.37	9.778%	$190.3221	$190.32	$190.30	$190.30
Purchase #6	$139.61	3.738%	$144.8286	$144.83	$144.85	$144.80
Purchase #7	$134.42	6.584%	$143.2702	$143.27	$143.25	$143.30
7 purchase totals =	$1,098.82		$1,196.8961	$1,196.90	$1,196.90	$1,196.90