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	$136.78	4.480%	$142.9077	$142.91	$142.90	$142.90
Purchase #2	$40.47	7.343%	$43.4417	$43.44	$43.45	$43.40
Purchase #3	$172.48	10.473%	$190.5438	$190.54	$190.55	$190.50
Purchase #4	$136.43	8.617%	$148.1862	$148.19	$148.20	$148.20
Purchase #5	$64.39	3.370%	$66.5599	$66.56	$66.55	$66.60
Purchase #6	$100.64	4.776%	$105.4466	$105.45	$105.45	$105.40
Purchase #7	$176.26	9.304%	$192.6592	$192.66	$192.65	$192.70
7 purchase totals =	$827.45		$889.7451	$889.75	$889.75	$889.70