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	$33.93	13.578%	$38.537	$38.54	$38.55	$38.50
Purchase #2	$97.43	6.602%	$103.8623	$103.86	$103.85	$103.90
Purchase #3	$151.70	8.734%	$164.9495	$164.95	$164.95	$164.90
Purchase #4	$22.72	7.867%	$24.5074	$24.51	$24.50	$24.50
Purchase #5	$180.44	13.466%	$204.7381	$204.74	$204.75	$204.70
Purchase #6	$73.86	4.613%	$77.2672	$77.27	$77.25	$77.30
Purchase #7	$182.87	9.726%	$200.6559	$200.66	$200.65	$200.70
7 purchase totals =	$742.95		$814.5174	$814.53	$814.50	$814.50