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	$50.92	13.614%	$57.8522	$57.85	$57.85	$57.90
Purchase #2	$100.72	8.218%	$108.9972	$109.00	$109.00	$109.00
Purchase #3	$218.37	4.324%	$227.8123	$227.81	$227.80	$227.80
Purchase #4	$126.55	8.387%	$137.1637	$137.16	$137.15	$137.20
Purchase #5	$173.55	7.837%	$187.1511	$187.15	$187.15	$187.20
Purchase #6	$71.34	12.452%	$80.2233	$80.22	$80.20	$80.20
Purchase #7	$164.32	4.776%	$172.1679	$172.17	$172.15	$172.20
7 purchase totals =	$905.77		$971.3677	$971.36	$971.30	$971.50