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	$133.57	6.193%	$141.842	$141.84	$141.85	$141.80
Purchase #2	$191.51	13.762%	$217.8656	$217.87	$217.85	$217.90
Purchase #3	$216.45	11.619%	$241.5993	$241.60	$241.60	$241.60
Purchase #4	$29.82	13.225%	$33.7637	$33.76	$33.75	$33.80
Purchase #5	$27.87	4.812%	$29.2111	$29.21	$29.20	$29.20
Purchase #6	$144.52	9.550%	$158.3217	$158.32	$158.30	$158.30
Purchase #7	$95.38	10.145%	$105.0563	$105.06	$105.05	$105.10
7 purchase totals =	$839.12		$927.6597	$927.66	$927.60	$927.70