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	$234.77	8.780%	$255.3828	$255.38	$255.40	$255.40
Purchase #2	$25.56	7.622%	$27.5082	$27.51	$27.50	$27.50
Purchase #3	$92.64	9.468%	$101.4112	$101.41	$101.40	$101.40
Purchase #4	$102.63	8.426%	$111.2776	$111.28	$111.30	$111.30
Purchase #5	$90.39	5.536%	$95.394	$95.39	$95.40	$95.40
Purchase #6	$135.78	11.201%	$150.9887	$150.99	$151.00	$151.00
Purchase #7	$125.82	12.366%	$141.3789	$141.38	$141.40	$141.40
7 purchase totals =	$807.59		$883.3414	$883.34	$883.40	$883.40