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	$111.44	10.269%	$122.8838	$122.88	$122.90	$122.90
Purchase #2	$42.50	7.739%	$45.7891	$45.79	$45.80	$45.80
Purchase #3	$105.51	3.786%	$109.5046	$109.50	$109.50	$109.50
Purchase #4	$116.86	7.825%	$126.0043	$126.00	$126.00	$126.00
Purchase #5	$37.75	11.758%	$42.1886	$42.19	$42.20	$42.20
Purchase #6	$155.54	13.390%	$176.3668	$176.37	$176.35	$176.40
Purchase #7	$109.78	7.314%	$117.8093	$117.81	$117.80	$117.80
7 purchase totals =	$679.38		$740.5465	$740.54	$740.55	$740.60