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	$137.43	9.412%	$150.3649	$150.36	$150.35	$150.40
Purchase #2	$31.47	5.540%	$33.2134	$33.21	$33.20	$33.20
Purchase #3	$76.98	13.783%	$87.5902	$87.59	$87.60	$87.60
Purchase #4	$227.97	11.665%	$254.5627	$254.56	$254.55	$254.60
Purchase #5	$119.59	10.615%	$132.2845	$132.28	$132.30	$132.30
Purchase #6	$78.81	9.173%	$86.0392	$86.04	$86.05	$86.00
Purchase #7	$43.54	6.553%	$46.3932	$46.39	$46.40	$46.40
7 purchase totals =	$715.79		$790.4481	$790.43	$790.45	$790.50