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	$35.83	6.298%	$38.0866	$38.09	$38.10	$38.10
Purchase #2	$70.35	3.607%	$72.8875	$72.89	$72.90	$72.90
Purchase #3	$76.92	12.522%	$86.5519	$86.55	$86.55	$86.60
Purchase #4	$22.74	6.372%	$24.189	$24.19	$24.20	$24.20
Purchase #5	$247.74	13.238%	$280.5358	$280.54	$280.55	$280.50
Purchase #6	$160.62	8.207%	$173.8021	$173.80	$173.80	$173.80
Purchase #7	$40.39	8.600%	$43.8635	$43.86	$43.85	$43.90
7 purchase totals =	$654.59		$719.9164	$719.92	$719.95	$720.00