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	$35.36	9.206%	$38.6152	$38.62	$38.60	$38.60
Purchase #2	$146.87	7.520%	$157.9146	$157.91	$157.90	$157.90
Purchase #3	$200.77	11.256%	$223.3687	$223.37	$223.35	$223.40
Purchase #4	$43.48	7.256%	$46.6349	$46.63	$46.65	$46.60
Purchase #5	$93.58	6.653%	$99.8059	$99.81	$99.80	$99.80
Purchase #6	$67.45	6.786%	$72.0272	$72.03	$72.05	$72.00
Purchase #7	$66.81	7.548%	$71.8528	$71.85	$71.85	$71.90
7 purchase totals =	$654.32		$710.2193	$710.22	$710.20	$710.20