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	$95.84	13.299%	$108.5858	$108.59	$108.60	$108.60
Purchase #2	$54.69	11.595%	$61.0313	$61.03	$61.05	$61.00
Purchase #3	$192.52	7.774%	$207.4865	$207.49	$207.50	$207.50
Purchase #4	$79.28	12.732%	$89.3739	$89.37	$89.35	$89.40
Purchase #5	$116.61	5.577%	$123.1133	$123.11	$123.10	$123.10
Purchase #6	$22.67	4.295%	$23.6437	$23.64	$23.65	$23.60
Purchase #7	$164.69	3.109%	$169.8102	$169.81	$169.80	$169.80
7 purchase totals =	$726.30		$783.0447	$783.04	$783.05	$783.00