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	$14.91	3.670%	$15.4572	$15.46	$15.45	$15.50
Purchase #2	$120.97	13.575%	$137.3917	$137.39	$137.40	$137.40
Purchase #3	$76.82	12.507%	$86.4279	$86.43	$86.45	$86.40
Purchase #4	$211.46	12.508%	$237.9094	$237.91	$237.90	$237.90
Purchase #5	$209.32	13.485%	$237.5468	$237.55	$237.55	$237.50
Purchase #6	$164.74	5.546%	$173.8765	$173.88	$173.90	$173.90
Purchase #7	$132.85	5.307%	$139.9003	$139.90	$139.90	$139.90
7 purchase totals =	$931.07		$1,028.5098	$1,028.52	$1,028.55	$1,028.50