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	$18.51	10.688%	$20.4883	$20.49	$20.50	$20.50
Purchase #2	$242.93	3.655%	$251.8091	$251.81	$251.80	$251.80
Purchase #3	$31.60	3.202%	$32.6118	$32.61	$32.60	$32.60
Purchase #4	$35.80	4.124%	$37.2764	$37.28	$37.30	$37.30
Purchase #5	$38.75	10.595%	$42.8556	$42.86	$42.85	$42.90
Purchase #6	$107.94	7.861%	$116.4252	$116.43	$116.45	$116.40
Purchase #7	$100.70	6.791%	$107.5385	$107.54	$107.55	$107.50
7 purchase totals =	$576.23		$609.0049	$609.02	$609.05	$609.00