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	$123.65	6.351%	$131.503	$131.50	$131.50	$131.50
Purchase #2	$175.96	11.322%	$195.8822	$195.88	$195.90	$195.90
Purchase #3	$38.74	12.581%	$43.6139	$43.61	$43.60	$43.60
Purchase #4	$165.51	11.379%	$184.3434	$184.34	$184.35	$184.30
Purchase #5	$175.39	10.583%	$193.9515	$193.95	$193.95	$194.00
Purchase #6	$164.99	5.363%	$173.8384	$173.84	$173.85	$173.80
Purchase #7	$161.58	9.636%	$177.1498	$177.15	$177.15	$177.10
7 purchase totals =	$1,005.82		$1,100.2822	$1,100.27	$1,100.30	$1,100.20