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	$40.67	6.794%	$43.4331	$43.43	$43.45	$43.40
Purchase #2	$245.89	11.776%	$274.846	$274.85	$274.85	$274.80
Purchase #3	$111.85	5.740%	$118.2702	$118.27	$118.25	$118.30
Purchase #4	$69.51	3.660%	$72.0541	$72.05	$72.05	$72.10
Purchase #5	$219.60	9.371%	$240.1787	$240.18	$240.20	$240.20
Purchase #6	$157.46	12.140%	$176.5756	$176.58	$176.60	$176.60
Purchase #7	$146.26	6.694%	$156.0506	$156.05	$156.05	$156.10
7 purchase totals =	$991.24		$1,081.4083	$1,081.41	$1,081.45	$1,081.50