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	$139.45	4.864%	$146.2328	$146.23	$146.25	$146.20
Purchase #2	$140.64	12.728%	$158.5407	$158.54	$158.55	$158.50
Purchase #3	$176.75	12.241%	$198.386	$198.39	$198.40	$198.40
Purchase #4	$171.39	11.798%	$191.6106	$191.61	$191.60	$191.60
Purchase #5	$138.91	13.598%	$157.799	$157.80	$157.80	$157.80
Purchase #6	$19.88	11.481%	$22.1624	$22.16	$22.15	$22.20
Purchase #7	$74.34	10.482%	$82.1323	$82.13	$82.15	$82.10
7 purchase totals =	$861.36		$956.8638	$956.86	$956.90	$956.80