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	$100.56	9.333%	$109.9453	$109.95	$109.95	$109.90
Purchase #2	$150.94	7.794%	$162.7043	$162.70	$162.70	$162.70
Purchase #3	$33.56	13.176%	$37.9819	$37.98	$38.00	$38.00
Purchase #4	$146.83	7.167%	$157.3533	$157.35	$157.35	$157.40
Purchase #5	$51.89	5.627%	$54.8099	$54.81	$54.80	$54.80
Purchase #6	$70.52	9.672%	$77.3407	$77.34	$77.35	$77.30
Purchase #7	$82.43	3.667%	$85.4527	$85.45	$85.45	$85.50
7 purchase totals =	$636.73		$685.5881	$685.58	$685.60	$685.60