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	$42.70	4.865%	$44.7774	$44.78	$44.80	$44.80
Purchase #2	$29.80	13.510%	$33.826	$33.83	$33.85	$33.80
Purchase #3	$219.71	13.534%	$249.4456	$249.45	$249.45	$249.40
Purchase #4	$243.47	5.397%	$256.6101	$256.61	$256.60	$256.60
Purchase #5	$25.50	8.787%	$27.7407	$27.74	$27.75	$27.70
Purchase #6	$127.25	12.731%	$143.4502	$143.45	$143.45	$143.50
Purchase #7	$89.49	12.729%	$100.8812	$100.88	$100.90	$100.90
7 purchase totals =	$777.92		$856.7312	$856.74	$856.80	$856.70