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	$31.60	4.295%	$32.9572	$32.96	$32.95	$33.00
Purchase #2	$43.35	13.627%	$49.2573	$49.26	$49.25	$49.30
Purchase #3	$127.57	13.696%	$145.042	$145.04	$145.05	$145.00
Purchase #4	$44.28	5.442%	$46.6897	$46.69	$46.70	$46.70
Purchase #5	$56.43	10.609%	$62.4167	$62.42	$62.40	$62.40
Purchase #6	$168.83	12.490%	$189.9169	$189.92	$189.90	$189.90
Purchase #7	$69.90	12.130%	$78.3789	$78.38	$78.40	$78.40
7 purchase totals =	$541.96		$604.6587	$604.67	$604.65	$604.70