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	$88.43	12.355%	$99.3555	$99.36	$99.35	$99.40
Purchase #2	$70.27	5.323%	$74.0105	$74.01	$74.00	$74.00
Purchase #3	$62.92	7.314%	$67.522	$67.52	$67.50	$67.50
Purchase #4	$130.90	5.475%	$138.0668	$138.07	$138.05	$138.10
Purchase #5	$57.59	10.514%	$63.645	$63.65	$63.65	$63.60
Purchase #6	$10.66	6.650%	$11.3689	$11.37	$11.35	$11.40
Purchase #7	$183.83	6.693%	$196.1337	$196.13	$196.15	$196.10
7 purchase totals =	$604.60		$650.1024	$650.11	$650.05	$650.10