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	$25.86	6.816%	$27.6226	$27.62	$27.60	$27.60
Purchase #2	$197.38	13.569%	$224.1625	$224.16	$224.15	$224.20
Purchase #3	$214.93	4.121%	$223.7873	$223.79	$223.80	$223.80
Purchase #4	$116.89	12.502%	$131.5036	$131.50	$131.50	$131.50
Purchase #5	$180.35	9.447%	$197.3877	$197.39	$197.40	$197.40
Purchase #6	$180.64	10.150%	$198.975	$198.98	$199.00	$199.00
Purchase #7	$144.84	13.770%	$164.7845	$164.78	$164.80	$164.80
7 purchase totals =	$1,060.89		$1,168.2232	$1,168.22	$1,168.25	$1,168.30