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	$164.81	12.473%	$185.3668	$185.37	$185.35	$185.40
Purchase #2	$239.65	12.778%	$270.2725	$270.27	$270.25	$270.30
Purchase #3	$214.31	13.336%	$242.8904	$242.89	$242.90	$242.90
Purchase #4	$142.36	7.652%	$153.2534	$153.25	$153.25	$153.30
Purchase #5	$241.60	5.639%	$255.2238	$255.22	$255.20	$255.20
Purchase #6	$105.87	3.846%	$109.9418	$109.94	$109.95	$109.90
Purchase #7	$11.54	13.779%	$13.1301	$13.13	$13.15	$13.10
7 purchase totals =	$1,120.14		$1,230.0788	$1,230.07	$1,230.05	$1,230.10