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	$40.80	5.155%	$42.9032	$42.90	$42.90	$42.90
Purchase #2	$134.61	12.395%	$151.2949	$151.29	$151.30	$151.30
Purchase #3	$174.75	3.481%	$180.833	$180.83	$180.85	$180.80
Purchase #4	$25.97	11.448%	$28.943	$28.94	$28.95	$28.90
Purchase #5	$66.34	9.812%	$72.8493	$72.85	$72.85	$72.80
Purchase #6	$164.26	4.838%	$172.2069	$172.21	$172.20	$172.20
Purchase #7	$103.64	12.308%	$116.396	$116.40	$116.40	$116.40
7 purchase totals =	$710.37		$765.4263	$765.42	$765.45	$765.30