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	$238.45	11.770%	$266.5156	$266.52	$266.50	$266.50
Purchase #2	$243.32	12.149%	$272.8809	$272.88	$272.90	$272.90
Purchase #3	$35.62	7.430%	$38.2666	$38.27	$38.25	$38.30
Purchase #4	$178.68	5.249%	$188.0589	$188.06	$188.05	$188.10
Purchase #5	$77.55	9.221%	$84.7009	$84.70	$84.70	$84.70
Purchase #6	$35.35	5.168%	$37.1769	$37.18	$37.20	$37.20
Purchase #7	$83.37	8.586%	$90.5281	$90.53	$90.55	$90.50
7 purchase totals =	$892.34		$978.1279	$978.14	$978.15	$978.20