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	$61.39	4.491%	$64.147	$64.15	$64.15	$64.10
Purchase #2	$248.49	8.690%	$270.0838	$270.08	$270.10	$270.10
Purchase #3	$76.26	3.485%	$78.9177	$78.92	$78.90	$78.90
Purchase #4	$165.63	3.484%	$171.4005	$171.40	$171.40	$171.40
Purchase #5	$103.85	12.387%	$116.7139	$116.71	$116.70	$116.70
Purchase #6	$117.86	11.510%	$131.4257	$131.43	$131.45	$131.40
Purchase #7	$147.59	3.702%	$153.0538	$153.05	$153.05	$153.10
7 purchase totals =	$921.07		$985.7424	$985.74	$985.75	$985.70