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	$38.45	9.408%	$42.0674	$42.07	$42.05	$42.10
Purchase #2	$43.80	3.160%	$45.1841	$45.18	$45.20	$45.20
Purchase #3	$229.88	13.801%	$261.6057	$261.61	$261.60	$261.60
Purchase #4	$132.77	5.587%	$140.1879	$140.19	$140.20	$140.20
Purchase #5	$113.82	11.525%	$126.9378	$126.94	$126.95	$126.90
Purchase #6	$43.32	12.673%	$48.8099	$48.81	$48.80	$48.80
Purchase #7	$249.52	9.822%	$274.0279	$274.03	$274.05	$274.00
7 purchase totals =	$851.56		$938.8207	$938.83	$938.85	$938.80