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	$138.77	12.750%	$156.4632	$156.46	$156.45	$156.50
Purchase #2	$104.54	5.154%	$109.928	$109.93	$109.95	$109.90
Purchase #3	$233.51	11.224%	$259.7192	$259.72	$259.70	$259.70
Purchase #4	$71.84	3.314%	$74.2208	$74.22	$74.20	$74.20
Purchase #5	$83.47	3.659%	$86.5242	$86.52	$86.50	$86.50
Purchase #6	$25.67	10.308%	$28.3161	$28.32	$28.30	$28.30
Purchase #7	$40.68	4.309%	$42.4329	$42.43	$42.45	$42.40
7 purchase totals =	$698.48		$757.6044	$757.60	$757.55	$757.50