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	$160.90	3.665%	$166.797	$166.80	$166.80	$166.80
Purchase #2	$162.69	10.215%	$179.3088	$179.31	$179.30	$179.30
Purchase #3	$130.54	5.281%	$137.4338	$137.43	$137.45	$137.40
Purchase #4	$66.72	11.615%	$74.4695	$74.47	$74.45	$74.50
Purchase #5	$104.37	6.763%	$111.4285	$111.43	$111.45	$111.40
Purchase #6	$77.26	10.655%	$85.4921	$85.49	$85.50	$85.50
Purchase #7	$12.59	5.140%	$13.2371	$13.24	$13.25	$13.20
7 purchase totals =	$715.07		$768.1668	$768.17	$768.20	$768.10