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	$127.61	6.725%	$136.1918	$136.19	$136.20	$136.20
Purchase #2	$35.29	8.845%	$38.4114	$38.41	$38.40	$38.40
Purchase #3	$179.50	9.562%	$196.6638	$196.66	$196.65	$196.70
Purchase #4	$179.61	3.606%	$186.0867	$186.09	$186.10	$186.10
Purchase #5	$85.99	11.458%	$95.8427	$95.84	$95.85	$95.80
Purchase #6	$86.42	11.579%	$96.4266	$96.43	$96.45	$96.40
Purchase #7	$132.46	10.182%	$145.9471	$145.95	$145.95	$145.90
7 purchase totals =	$826.88		$895.5701	$895.57	$895.60	$895.50