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	$153.69	12.270%	$172.5478	$172.55	$172.55	$172.50
Purchase #2	$243.34	6.226%	$258.4903	$258.49	$258.50	$258.50
Purchase #3	$16.92	13.763%	$19.2487	$19.25	$19.25	$19.20
Purchase #4	$159.93	6.871%	$170.9188	$170.92	$170.90	$170.90
Purchase #5	$60.37	8.140%	$65.2841	$65.28	$65.30	$65.30
Purchase #6	$43.81	8.624%	$47.5882	$47.59	$47.60	$47.60
Purchase #7	$20.50	6.495%	$21.8315	$21.83	$21.85	$21.80
7 purchase totals =	$698.56		$755.9094	$755.91	$755.95	$755.80