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	$76.70	3.834%	$79.6407	$79.64	$79.65	$79.60
Purchase #2	$20.53	3.282%	$21.2038	$21.20	$21.20	$21.20
Purchase #3	$25.65	4.857%	$26.8958	$26.90	$26.90	$26.90
Purchase #4	$80.27	11.496%	$89.4978	$89.50	$89.50	$89.50
Purchase #5	$160.84	7.455%	$172.8306	$172.83	$172.85	$172.80
Purchase #6	$51.87	11.686%	$57.9315	$57.93	$57.95	$57.90
Purchase #7	$117.58	4.839%	$123.2697	$123.27	$123.25	$123.30
7 purchase totals =	$533.44		$571.2699	$571.27	$571.30	$571.20