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	$92.99	11.106%	$103.3175	$103.32	$103.30	$103.30
Purchase #2	$103.30	5.577%	$109.061	$109.06	$109.05	$109.10
Purchase #3	$41.34	5.509%	$43.6174	$43.62	$43.60	$43.60
Purchase #4	$147.73	3.669%	$153.1502	$153.15	$153.15	$153.20
Purchase #5	$99.85	12.334%	$112.1655	$112.17	$112.15	$112.20
Purchase #6	$187.45	5.660%	$198.0597	$198.06	$198.05	$198.10
Purchase #7	$35.92	10.277%	$39.6115	$39.61	$39.60	$39.60
7 purchase totals =	$708.58		$758.9828	$758.99	$758.90	$759.10