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	$126.64	8.146%	$136.9561	$136.96	$136.95	$137.00
Purchase #2	$32.56	6.284%	$34.6061	$34.61	$34.60	$34.60
Purchase #3	$83.25	8.385%	$90.2305	$90.23	$90.25	$90.20
Purchase #4	$60.43	8.612%	$65.6342	$65.63	$65.65	$65.60
Purchase #5	$199.83	4.393%	$208.6085	$208.61	$208.60	$208.60
Purchase #6	$33.65	10.777%	$37.2765	$37.28	$37.30	$37.30
Purchase #7	$221.82	11.304%	$246.8945	$246.89	$246.90	$246.90
7 purchase totals =	$758.18		$820.2064	$820.21	$820.25	$820.20