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	$103.47	13.211%	$117.1394	$117.14	$117.15	$117.10
Purchase #2	$109.87	6.715%	$117.2478	$117.25	$117.25	$117.20
Purchase #3	$91.62	9.190%	$100.0399	$100.04	$100.05	$100.00
Purchase #4	$42.71	6.102%	$45.3162	$45.32	$45.30	$45.30
Purchase #5	$30.37	11.142%	$33.7538	$33.75	$33.75	$33.80
Purchase #6	$137.96	9.366%	$150.8813	$150.88	$150.90	$150.90
Purchase #7	$104.81	12.762%	$118.1859	$118.19	$118.20	$118.20
7 purchase totals =	$620.81		$682.5643	$682.57	$682.60	$682.50