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	$103.50	13.315%	$117.281	$117.28	$117.30	$117.30
Purchase #2	$43.53	4.597%	$45.5311	$45.53	$45.55	$45.50
Purchase #3	$8.65	9.845%	$9.5016	$9.50	$9.50	$9.50
Purchase #4	$148.78	6.545%	$158.5177	$158.52	$158.50	$158.50
Purchase #5	$63.69	3.449%	$65.8867	$65.89	$65.90	$65.90
Purchase #6	$82.60	5.603%	$87.2281	$87.23	$87.25	$87.20
Purchase #7	$127.86	7.133%	$136.9803	$136.98	$137.00	$137.00
7 purchase totals =	$578.61		$620.9265	$620.93	$621.00	$620.90