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	$34.27	7.654%	$36.893	$36.89	$36.90	$36.90
Purchase #2	$54.65	4.297%	$56.9983	$57.00	$57.00	$57.00
Purchase #3	$113.72	13.324%	$128.8721	$128.87	$128.85	$128.90
Purchase #4	$233.40	7.348%	$250.5502	$250.55	$250.55	$250.60
Purchase #5	$6.66	4.180%	$6.9384	$6.94	$6.95	$6.90
Purchase #6	$49.88	8.376%	$54.0579	$54.06	$54.05	$54.10
Purchase #7	$42.32	5.235%	$44.5355	$44.54	$44.55	$44.50
7 purchase totals =	$534.90		$578.8454	$578.85	$578.85	$578.90