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	$96.73	6.720%	$103.2303	$103.23	$103.25	$103.20
Purchase #2	$150.29	5.773%	$158.9662	$158.97	$158.95	$159.00
Purchase #3	$248.94	12.293%	$279.5422	$279.54	$279.55	$279.50
Purchase #4	$29.97	9.149%	$32.712	$32.71	$32.70	$32.70
Purchase #5	$164.34	12.191%	$184.3747	$184.37	$184.35	$184.40
Purchase #6	$228.39	5.654%	$241.3032	$241.30	$241.30	$241.30
Purchase #7	$102.69	6.397%	$109.2591	$109.26	$109.25	$109.30
7 purchase totals =	$1,021.35		$1,109.3877	$1,109.38	$1,109.35	$1,109.40