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	$123.25	6.631%	$131.4227	$131.42	$131.40	$131.40
Purchase #2	$157.69	3.602%	$163.37	$163.37	$163.35	$163.40
Purchase #3	$247.35	5.741%	$261.5504	$261.55	$261.55	$261.60
Purchase #4	$140.52	10.546%	$155.3392	$155.34	$155.35	$155.30
Purchase #5	$174.81	13.576%	$198.5422	$198.54	$198.55	$198.50
Purchase #6	$214.78	7.475%	$230.8348	$230.83	$230.85	$230.80
Purchase #7	$55.27	7.184%	$59.2406	$59.24	$59.25	$59.20
7 purchase totals =	$1,113.67		$1,200.2999	$1,200.29	$1,200.30	$1,200.20