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	$144.67	12.328%	$162.5049	$162.50	$162.50	$162.50
Purchase #2	$205.61	12.438%	$231.1838	$231.18	$231.20	$231.20
Purchase #3	$27.94	10.763%	$30.9472	$30.95	$30.95	$30.90
Purchase #4	$111.82	9.647%	$122.6073	$122.61	$122.60	$122.60
Purchase #5	$185.96	7.409%	$199.7378	$199.74	$199.75	$199.70
Purchase #6	$91.52	9.830%	$100.5164	$100.52	$100.50	$100.50
Purchase #7	$49.88	6.209%	$52.977	$52.98	$53.00	$53.00
7 purchase totals =	$817.40		$900.4744	$900.48	$900.50	$900.40