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	$82.84	8.862%	$90.1813	$90.18	$90.20	$90.20
Purchase #2	$63.94	5.516%	$67.4669	$67.47	$67.45	$67.50
Purchase #3	$100.50	7.308%	$107.8445	$107.84	$107.85	$107.80
Purchase #4	$62.38	3.842%	$64.7766	$64.78	$64.80	$64.80
Purchase #5	$186.58	7.335%	$200.2656	$200.27	$200.25	$200.30
Purchase #6	$60.96	7.290%	$65.404	$65.40	$65.40	$65.40
Purchase #7	$158.47	3.436%	$163.915	$163.92	$163.90	$163.90
7 purchase totals =	$715.67		$759.8539	$759.86	$759.85	$759.90