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	$39.57	8.858%	$43.0751	$43.08	$43.10	$43.10
Purchase #2	$39.39	5.334%	$41.4911	$41.49	$41.50	$41.50
Purchase #3	$178.59	7.138%	$191.3378	$191.34	$191.35	$191.30
Purchase #4	$137.29	10.845%	$152.1791	$152.18	$152.20	$152.20
Purchase #5	$223.40	11.647%	$249.4194	$249.42	$249.40	$249.40
Purchase #6	$11.56	13.722%	$13.1463	$13.15	$13.15	$13.10
Purchase #7	$131.94	11.709%	$147.3889	$147.39	$147.40	$147.40
7 purchase totals =	$761.74		$838.0377	$838.05	$838.10	$838.00