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	$122.42	7.815%	$131.9871	$131.99	$132.00	$132.00
Purchase #2	$29.34	10.132%	$32.3127	$32.31	$32.30	$32.30
Purchase #3	$137.99	3.552%	$142.8914	$142.89	$142.90	$142.90
Purchase #4	$155.37	11.790%	$173.6881	$173.69	$173.70	$173.70
Purchase #5	$99.60	9.368%	$108.9305	$108.93	$108.95	$108.90
Purchase #6	$85.50	5.716%	$90.3872	$90.39	$90.40	$90.40
Purchase #7	$234.50	9.608%	$257.0308	$257.03	$257.05	$257.00
7 purchase totals =	$864.72		$937.2278	$937.23	$937.30	$937.20