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	$13.57	12.432%	$15.257	$15.26	$15.25	$15.30
Purchase #2	$146.69	3.206%	$151.3929	$151.39	$151.40	$151.40
Purchase #3	$86.85	3.763%	$90.1182	$90.12	$90.10	$90.10
Purchase #4	$15.42	11.844%	$17.2463	$17.25	$17.25	$17.20
Purchase #5	$125.82	10.733%	$139.3243	$139.32	$139.30	$139.30
Purchase #6	$215.54	10.602%	$238.3916	$238.39	$238.40	$238.40
Purchase #7	$65.42	8.705%	$71.1148	$71.11	$71.10	$71.10
7 purchase totals =	$669.31		$722.8451	$722.84	$722.80	$722.80