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	$241.29	6.452%	$256.858	$256.86	$256.85	$256.90
Purchase #2	$186.78	3.153%	$192.6692	$192.67	$192.65	$192.70
Purchase #3	$223.77	4.703%	$234.2939	$234.29	$234.30	$234.30
Purchase #4	$76.55	6.146%	$81.2548	$81.25	$81.25	$81.30
Purchase #5	$37.64	12.151%	$42.2136	$42.21	$42.20	$42.20
Purchase #6	$69.93	12.473%	$78.6524	$78.65	$78.65	$78.70
Purchase #7	$128.60	3.225%	$132.7474	$132.75	$132.75	$132.70
7 purchase totals =	$964.56		$1,018.6893	$1,018.68	$1,018.65	$1,018.80