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	$51.81	9.228%	$56.591	$56.59	$56.60	$56.60
Purchase #2	$234.65	13.397%	$266.0861	$266.09	$266.10	$266.10
Purchase #3	$85.89	3.830%	$89.1796	$89.18	$89.20	$89.20
Purchase #4	$139.39	9.317%	$152.377	$152.38	$152.40	$152.40
Purchase #5	$87.71	3.200%	$90.5167	$90.52	$90.50	$90.50
Purchase #6	$241.54	5.648%	$255.1822	$255.18	$255.20	$255.20
Purchase #7	$236.99	7.516%	$254.8022	$254.80	$254.80	$254.80
7 purchase totals =	$1,077.98		$1,164.7348	$1,164.74	$1,164.80	$1,164.80