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	$12.63	6.295%	$13.4251	$13.43	$13.45	$13.40
Purchase #2	$41.28	7.249%	$44.2724	$44.27	$44.25	$44.30
Purchase #3	$80.83	12.137%	$90.6403	$90.64	$90.65	$90.60
Purchase #4	$232.25	7.549%	$249.7826	$249.78	$249.80	$249.80
Purchase #5	$10.73	11.134%	$11.9247	$11.92	$11.90	$11.90
Purchase #6	$48.80	8.157%	$52.7806	$52.78	$52.80	$52.80
Purchase #7	$134.35	3.773%	$139.419	$139.42	$139.40	$139.40
7 purchase totals =	$560.87		$602.2447	$602.24	$602.25	$602.20