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	$34.96	8.622%	$37.9743	$37.97	$37.95	$38.00
Purchase #2	$155.37	8.505%	$168.5842	$168.58	$168.60	$168.60
Purchase #3	$97.84	5.314%	$103.0392	$103.04	$103.05	$103.00
Purchase #4	$115.29	11.819%	$128.9161	$128.92	$128.90	$128.90
Purchase #5	$11.33	13.484%	$12.8577	$12.86	$12.85	$12.90
Purchase #6	$137.34	12.685%	$154.7616	$154.76	$154.75	$154.80
Purchase #7	$60.71	5.124%	$63.8208	$63.82	$63.80	$63.80
7 purchase totals =	$612.84		$669.9539	$669.95	$669.90	$670.00