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	$87.78	4.357%	$91.6046	$91.60	$91.60	$91.60
Purchase #2	$134.78	10.304%	$148.6677	$148.67	$148.65	$148.70
Purchase #3	$35.32	3.208%	$36.4531	$36.45	$36.45	$36.50
Purchase #4	$159.94	5.225%	$168.2969	$168.30	$168.30	$168.30
Purchase #5	$100.75	4.578%	$105.3623	$105.36	$105.35	$105.40
Purchase #6	$192.54	7.293%	$206.5819	$206.58	$206.60	$206.60
Purchase #7	$159.72	13.343%	$181.0314	$181.03	$181.05	$181.00
7 purchase totals =	$870.83		$937.9979	$937.99	$938.00	$938.10