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	$38.50	12.254%	$43.2178	$43.22	$43.20	$43.20
Purchase #2	$155.74	13.454%	$176.6933	$176.69	$176.70	$176.70
Purchase #3	$52.82	9.799%	$57.9958	$58.00	$58.00	$58.00
Purchase #4	$226.30	3.795%	$234.8881	$234.89	$234.90	$234.90
Purchase #5	$37.37	12.392%	$42.0009	$42.00	$42.00	$42.00
Purchase #6	$13.60	10.746%	$15.0615	$15.06	$15.05	$15.10
Purchase #7	$106.26	10.651%	$117.5778	$117.58	$117.60	$117.60
7 purchase totals =	$630.59		$687.4352	$687.44	$687.45	$687.50