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	$128.93	11.743%	$144.0702	$144.07	$144.05	$144.10
Purchase #2	$145.37	3.496%	$150.4521	$150.45	$150.45	$150.50
Purchase #3	$35.71	6.263%	$37.9465	$37.95	$37.95	$37.90
Purchase #4	$20.57	5.347%	$21.6699	$21.67	$21.65	$21.70
Purchase #5	$204.72	9.569%	$224.3097	$224.31	$224.30	$224.30
Purchase #6	$228.60	9.706%	$250.7879	$250.79	$250.80	$250.80
Purchase #7	$143.79	10.455%	$158.8232	$158.82	$158.80	$158.80
7 purchase totals =	$907.69		$988.0595	$988.06	$988.00	$988.10