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	$81.85	10.278%	$90.2625	$90.26	$90.25	$90.30
Purchase #2	$198.67	13.350%	$225.1924	$225.19	$225.20	$225.20
Purchase #3	$148.47	3.591%	$153.8016	$153.80	$153.80	$153.80
Purchase #4	$144.78	10.570%	$160.0832	$160.08	$160.10	$160.10
Purchase #5	$41.89	5.550%	$44.2149	$44.21	$44.20	$44.20
Purchase #6	$92.29	12.163%	$103.5152	$103.52	$103.50	$103.50
Purchase #7	$62.54	6.852%	$66.8252	$66.83	$66.85	$66.80
7 purchase totals =	$770.49		$843.8950	$843.89	$843.90	$843.90