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	$44.52	10.673%	$49.2716	$49.27	$49.25	$49.30
Purchase #2	$143.83	3.242%	$148.493	$148.49	$148.50	$148.50
Purchase #3	$106.94	10.581%	$118.2553	$118.26	$118.25	$118.30
Purchase #4	$87.84	3.393%	$90.8204	$90.82	$90.80	$90.80
Purchase #5	$103.40	7.535%	$111.1912	$111.19	$111.20	$111.20
Purchase #6	$116.70	4.234%	$121.6411	$121.64	$121.65	$121.60
Purchase #7	$57.53	11.625%	$64.2179	$64.22	$64.20	$64.20
7 purchase totals =	$660.76		$703.8905	$703.89	$703.85	$703.90