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	$6.60	11.505%	$7.3593	$7.36	$7.35	$7.40
Purchase #2	$40.45	10.237%	$44.5909	$44.59	$44.60	$44.60
Purchase #3	$122.73	11.265%	$136.5555	$136.56	$136.55	$136.60
Purchase #4	$45.50	8.678%	$49.4485	$49.45	$49.45	$49.40
Purchase #5	$181.63	9.861%	$199.5405	$199.54	$199.55	$199.50
Purchase #6	$59.31	12.150%	$66.5162	$66.52	$66.50	$66.50
Purchase #7	$69.84	12.280%	$78.4164	$78.42	$78.40	$78.40
7 purchase totals =	$526.06		$582.4273	$582.44	$582.40	$582.40