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	$29.45	10.845%	$32.6439	$32.64	$32.65	$32.60
Purchase #2	$28.59	4.628%	$29.9131	$29.91	$29.90	$29.90
Purchase #3	$229.82	10.225%	$253.3191	$253.32	$253.30	$253.30
Purchase #4	$242.30	12.528%	$272.6553	$272.66	$272.65	$272.70
Purchase #5	$107.52	12.433%	$120.888	$120.89	$120.90	$120.90
Purchase #6	$8.92	9.801%	$9.7942	$9.79	$9.80	$9.80
Purchase #7	$82.32	10.172%	$90.6936	$90.69	$90.70	$90.70
7 purchase totals =	$728.92		$809.9072	$809.90	$809.90	$809.90