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	$239.52	13.732%	$272.4109	$272.41	$272.40	$272.40
Purchase #2	$10.60	6.585%	$11.298	$11.30	$11.30	$11.30
Purchase #3	$31.44	3.447%	$32.5237	$32.52	$32.50	$32.50
Purchase #4	$132.34	3.709%	$137.2485	$137.25	$137.25	$137.20
Purchase #5	$121.80	7.663%	$131.1335	$131.13	$131.15	$131.10
Purchase #6	$138.51	8.713%	$150.5784	$150.58	$150.60	$150.60
Purchase #7	$144.83	5.676%	$153.0506	$153.05	$153.05	$153.10
7 purchase totals =	$819.04		$888.2436	$888.24	$888.25	$888.20