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	$58.49	13.553%	$66.4171	$66.42	$66.40	$66.40
Purchase #2	$238.31	12.106%	$267.1598	$267.16	$267.15	$267.20
Purchase #3	$153.65	7.149%	$164.6344	$164.63	$164.65	$164.60
Purchase #4	$102.77	13.786%	$116.9379	$116.94	$116.95	$116.90
Purchase #5	$66.46	6.853%	$71.0145	$71.01	$71.00	$71.00
Purchase #6	$168.76	6.196%	$179.2164	$179.22	$179.20	$179.20
Purchase #7	$42.69	12.495%	$48.0241	$48.02	$48.00	$48.00
7 purchase totals =	$831.13		$913.4042	$913.40	$913.35	$913.30