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	$32.96	13.547%	$37.4251	$37.43	$37.45	$37.40
Purchase #2	$138.26	3.518%	$143.124	$143.12	$143.10	$143.10
Purchase #3	$43.37	9.545%	$47.5097	$47.51	$47.50	$47.50
Purchase #4	$101.29	10.357%	$111.7806	$111.78	$111.80	$111.80
Purchase #5	$95.31	9.516%	$104.3797	$104.38	$104.40	$104.40
Purchase #6	$216.62	7.288%	$232.4073	$232.41	$232.40	$232.40
Purchase #7	$147.44	4.805%	$154.5245	$154.52	$154.50	$154.50
7 purchase totals =	$775.25		$831.1509	$831.15	$831.15	$831.10