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	$39.95	11.373%	$44.4935	$44.49	$44.50	$44.50
Purchase #2	$167.96	9.458%	$183.8457	$183.85	$183.85	$183.80
Purchase #3	$116.55	13.738%	$132.5616	$132.56	$132.55	$132.60
Purchase #4	$43.79	6.350%	$46.5707	$46.57	$46.55	$46.60
Purchase #5	$98.30	13.104%	$111.1812	$111.18	$111.20	$111.20
Purchase #6	$177.85	10.587%	$196.679	$196.68	$196.70	$196.70
Purchase #7	$231.61	13.703%	$263.3475	$263.35	$263.35	$263.30
7 purchase totals =	$876.01		$978.6792	$978.68	$978.70	$978.70