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	$40.99	5.521%	$43.2531	$43.25	$43.25	$43.30
Purchase #2	$70.47	10.807%	$78.0857	$78.09	$78.10	$78.10
Purchase #3	$227.28	6.165%	$241.2918	$241.29	$241.30	$241.30
Purchase #4	$90.66	9.644%	$99.4033	$99.40	$99.40	$99.40
Purchase #5	$125.32	5.821%	$132.6149	$132.61	$132.60	$132.60
Purchase #6	$133.84	7.711%	$144.1604	$144.16	$144.15	$144.20
Purchase #7	$91.29	13.715%	$103.8104	$103.81	$103.80	$103.80
7 purchase totals =	$779.85		$842.6196	$842.61	$842.60	$842.70