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	$117.36	12.397%	$131.9091	$131.91	$131.90	$131.90
Purchase #2	$234.59	13.401%	$266.0274	$266.03	$266.05	$266.00
Purchase #3	$43.93	12.704%	$49.5109	$49.51	$49.50	$49.50
Purchase #4	$221.46	7.604%	$238.2998	$238.30	$238.30	$238.30
Purchase #5	$13.93	8.438%	$15.1054	$15.11	$15.10	$15.10
Purchase #6	$114.54	11.373%	$127.5666	$127.57	$127.55	$127.60
Purchase #7	$124.71	10.202%	$137.4329	$137.43	$137.45	$137.40
7 purchase totals =	$870.52		$965.8521	$965.86	$965.85	$965.80