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	$33.87	11.640%	$37.8125	$37.81	$37.80	$37.80
Purchase #2	$123.91	7.284%	$132.9356	$132.94	$132.95	$132.90
Purchase #3	$34.93	5.708%	$36.9238	$36.92	$36.90	$36.90
Purchase #4	$155.75	11.323%	$173.3856	$173.39	$173.40	$173.40
Purchase #5	$131.48	4.626%	$137.5623	$137.56	$137.55	$137.60
Purchase #6	$53.86	10.229%	$59.3693	$59.37	$59.35	$59.40
Purchase #7	$192.84	9.366%	$210.9014	$210.90	$210.90	$210.90
7 purchase totals =	$726.64		$788.8905	$788.89	$788.85	$788.90