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	$76.26	8.168%	$82.4889	$82.49	$82.50	$82.50
Purchase #2	$52.47	13.558%	$59.5839	$59.58	$59.60	$59.60
Purchase #3	$78.86	13.861%	$89.7908	$89.79	$89.80	$89.80
Purchase #4	$72.27	13.509%	$82.033	$82.03	$82.05	$82.00
Purchase #5	$159.63	10.672%	$176.6657	$176.67	$176.65	$176.70
Purchase #6	$224.33	3.762%	$232.7693	$232.77	$232.75	$232.80
Purchase #7	$75.38	3.771%	$78.2226	$78.22	$78.20	$78.20
7 purchase totals =	$739.20		$801.5542	$801.55	$801.55	$801.60