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	$27.94	12.621%	$31.4663	$31.47	$31.45	$31.50
Purchase #2	$164.96	9.397%	$180.4613	$180.46	$180.45	$180.50
Purchase #3	$132.76	11.172%	$147.5919	$147.59	$147.60	$147.60
Purchase #4	$173.26	3.667%	$179.6134	$179.61	$179.60	$179.60
Purchase #5	$19.69	7.518%	$21.1703	$21.17	$21.15	$21.20
Purchase #6	$69.88	11.705%	$78.0595	$78.06	$78.05	$78.10
Purchase #7	$91.89	9.869%	$100.9586	$100.96	$100.95	$101.00
7 purchase totals =	$680.38		$739.3213	$739.32	$739.25	$739.50