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	$157.25	8.430%	$170.5062	$170.51	$170.50	$170.50
Purchase #2	$193.34	9.181%	$211.0905	$211.09	$211.10	$211.10
Purchase #3	$78.38	10.690%	$86.7588	$86.76	$86.75	$86.80
Purchase #4	$11.83	11.290%	$13.1656	$13.17	$13.15	$13.20
Purchase #5	$180.85	8.819%	$196.7992	$196.80	$196.80	$196.80
Purchase #6	$47.93	10.636%	$53.0278	$53.03	$53.05	$53.00
Purchase #7	$95.37	10.357%	$105.2475	$105.25	$105.25	$105.20
7 purchase totals =	$764.95		$836.5956	$836.61	$836.60	$836.60