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	$122.98	10.596%	$136.011	$136.01	$136.00	$136.00
Purchase #2	$235.67	7.210%	$252.6618	$252.66	$252.65	$252.70
Purchase #3	$129.86	9.644%	$142.3837	$142.38	$142.40	$142.40
Purchase #4	$39.33	10.232%	$43.3542	$43.35	$43.35	$43.40
Purchase #5	$76.94	12.231%	$86.3505	$86.35	$86.35	$86.40
Purchase #6	$160.39	7.560%	$172.5155	$172.52	$172.50	$172.50
Purchase #7	$231.64	13.484%	$262.8743	$262.87	$262.85	$262.90
7 purchase totals =	$996.81		$1,096.1510	$1,096.14	$1,096.10	$1,096.30