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	$138.85	4.865%	$145.6051	$145.61	$145.60	$145.60
Purchase #2	$146.37	4.378%	$152.7781	$152.78	$152.80	$152.80
Purchase #3	$176.52	6.641%	$188.2427	$188.24	$188.25	$188.20
Purchase #4	$226.48	9.311%	$247.5676	$247.57	$247.55	$247.60
Purchase #5	$43.86	9.760%	$48.1407	$48.14	$48.15	$48.10
Purchase #6	$63.39	13.430%	$71.9033	$71.90	$71.90	$71.90
Purchase #7	$160.76	7.517%	$172.8443	$172.84	$172.85	$172.80
7 purchase totals =	$956.23		$1,027.0818	$1,027.08	$1,027.10	$1,027.00