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	$130.31	12.447%	$146.5297	$146.53	$146.55	$146.50
Purchase #2	$210.95	9.425%	$230.832	$230.83	$230.85	$230.80
Purchase #3	$128.57	7.716%	$138.4905	$138.49	$138.50	$138.50
Purchase #4	$66.44	5.709%	$70.2331	$70.23	$70.25	$70.20
Purchase #5	$172.59	9.615%	$189.1845	$189.18	$189.20	$189.20
Purchase #6	$52.25	4.156%	$54.4215	$54.42	$54.40	$54.40
Purchase #7	$84.35	6.455%	$89.7948	$89.79	$89.80	$89.80
7 purchase totals =	$845.46		$919.4861	$919.47	$919.55	$919.40