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	$186.65	6.626%	$199.0174	$199.02	$199.00	$199.00
Purchase #2	$41.49	9.547%	$45.4511	$45.45	$45.45	$45.50
Purchase #3	$135.32	5.310%	$142.5055	$142.51	$142.50	$142.50
Purchase #4	$9.78	11.161%	$10.8715	$10.87	$10.85	$10.90
Purchase #5	$163.43	3.505%	$169.1582	$169.16	$169.15	$169.20
Purchase #6	$115.63	10.334%	$127.5792	$127.58	$127.60	$127.60
Purchase #7	$218.53	10.661%	$241.8275	$241.83	$241.85	$241.80
7 purchase totals =	$870.83		$936.4104	$936.42	$936.40	$936.50