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	$153.26	5.300%	$161.3828	$161.38	$161.40	$161.40
Purchase #2	$60.74	11.368%	$67.6449	$67.64	$67.65	$67.60
Purchase #3	$56.80	4.721%	$59.4815	$59.48	$59.50	$59.50
Purchase #4	$228.99	12.500%	$257.6138	$257.61	$257.60	$257.60
Purchase #5	$113.85	10.329%	$125.6096	$125.61	$125.60	$125.60
Purchase #6	$97.79	13.844%	$111.328	$111.33	$111.35	$111.30
Purchase #7	$84.42	3.268%	$87.1788	$87.18	$87.20	$87.20
7 purchase totals =	$795.85		$870.2394	$870.23	$870.30	$870.20