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	$126.56	10.222%	$139.497	$139.50	$139.50	$139.50
Purchase #2	$100.97	7.773%	$108.8184	$108.82	$108.80	$108.80
Purchase #3	$202.54	9.538%	$221.8583	$221.86	$221.85	$221.90
Purchase #4	$133.37	4.470%	$139.3316	$139.33	$139.35	$139.30
Purchase #5	$232.75	4.775%	$243.8638	$243.86	$243.85	$243.90
Purchase #6	$116.54	13.684%	$132.4873	$132.49	$132.50	$132.50
Purchase #7	$238.39	8.349%	$258.2932	$258.29	$258.30	$258.30
7 purchase totals =	$1,151.12		$1,244.1496	$1,244.15	$1,244.15	$1,244.20