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	$50.92	5.230%	$53.5831	$53.58	$53.60	$53.60
Purchase #2	$174.52	11.697%	$194.9336	$194.93	$194.95	$194.90
Purchase #3	$247.79	11.351%	$275.9166	$275.92	$275.90	$275.90
Purchase #4	$95.71	12.849%	$108.0078	$108.01	$108.00	$108.00
Purchase #5	$41.34	5.614%	$43.6608	$43.66	$43.65	$43.70
Purchase #6	$208.85	9.414%	$228.5111	$228.51	$228.50	$228.50
Purchase #7	$81.57	6.498%	$86.8704	$86.87	$86.85	$86.90
7 purchase totals =	$900.70		$991.4834	$991.48	$991.45	$991.50