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	$189.33	13.477%	$214.846	$214.85	$214.85	$214.80
Purchase #2	$69.27	6.140%	$73.5232	$73.52	$73.50	$73.50
Purchase #3	$12.79	6.819%	$13.6622	$13.66	$13.65	$13.70
Purchase #4	$52.92	13.180%	$59.8949	$59.89	$59.90	$59.90
Purchase #5	$67.66	10.719%	$74.9125	$74.91	$74.90	$74.90
Purchase #6	$152.62	9.217%	$166.687	$166.69	$166.70	$166.70
Purchase #7	$40.49	9.856%	$44.4807	$44.48	$44.50	$44.50
7 purchase totals =	$585.08		$648.0065	$648.00	$648.00	$648.00