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	$94.51	4.762%	$99.0106	$99.01	$99.00	$99.00
Purchase #2	$200.40	12.152%	$224.7526	$224.75	$224.75	$224.80
Purchase #3	$144.68	9.378%	$158.2481	$158.25	$158.25	$158.20
Purchase #4	$216.87	3.657%	$224.8009	$224.80	$224.80	$224.80
Purchase #5	$214.91	3.485%	$222.3996	$222.40	$222.40	$222.40
Purchase #6	$41.26	8.795%	$44.8888	$44.89	$44.90	$44.90
Purchase #7	$205.82	5.783%	$217.7226	$217.72	$217.70	$217.70
7 purchase totals =	$1,118.45		$1,191.8232	$1,191.82	$1,191.80	$1,191.80