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	$88.47	13.238%	$100.1817	$100.18	$100.20	$100.20
Purchase #2	$158.64	4.621%	$165.9708	$165.97	$165.95	$166.00
Purchase #3	$66.41	3.204%	$68.5378	$68.54	$68.55	$68.50
Purchase #4	$117.51	11.641%	$131.1893	$131.19	$131.20	$131.20
Purchase #5	$190.86	13.480%	$216.5879	$216.59	$216.60	$216.60
Purchase #6	$60.70	8.383%	$65.7885	$65.79	$65.80	$65.80
Purchase #7	$78.82	5.108%	$82.8461	$82.85	$82.85	$82.80
7 purchase totals =	$761.41		$831.1021	$831.11	$831.15	$831.10