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	$138.91	11.850%	$155.3708	$155.37	$155.35	$155.40
Purchase #2	$43.80	4.837%	$45.9186	$45.92	$45.90	$45.90
Purchase #3	$18.79	9.390%	$20.5544	$20.55	$20.55	$20.60
Purchase #4	$238.98	13.319%	$270.8097	$270.81	$270.80	$270.80
Purchase #5	$42.38	10.643%	$46.8905	$46.89	$46.90	$46.90
Purchase #6	$40.76	9.389%	$44.587	$44.59	$44.60	$44.60
Purchase #7	$73.29	3.796%	$76.0721	$76.07	$76.05	$76.10
7 purchase totals =	$596.91		$660.2031	$660.20	$660.15	$660.30