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	$166.69	11.603%	$186.031	$186.03	$186.05	$186.00
Purchase #2	$130.56	13.715%	$148.4663	$148.47	$148.45	$148.50
Purchase #3	$200.74	10.668%	$222.1549	$222.15	$222.15	$222.20
Purchase #4	$221.49	12.542%	$249.2693	$249.27	$249.25	$249.30
Purchase #5	$134.67	3.678%	$139.6232	$139.62	$139.60	$139.60
Purchase #6	$192.83	10.644%	$213.3548	$213.35	$213.35	$213.40
Purchase #7	$123.60	3.334%	$127.7208	$127.72	$127.70	$127.70
7 purchase totals =	$1,170.58		$1,286.6203	$1,286.61	$1,286.55	$1,286.70