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	$29.66	12.761%	$33.4449	$33.44	$33.45	$33.40
Purchase #2	$225.31	7.525%	$242.2646	$242.26	$242.25	$242.30
Purchase #3	$79.31	10.825%	$87.8953	$87.90	$87.90	$87.90
Purchase #4	$120.64	6.487%	$128.4659	$128.47	$128.45	$128.50
Purchase #5	$219.49	10.294%	$242.0843	$242.08	$242.10	$242.10
Purchase #6	$117.53	9.348%	$128.5167	$128.52	$128.50	$128.50
Purchase #7	$34.60	10.547%	$38.2493	$38.25	$38.25	$38.20
7 purchase totals =	$826.54		$900.9210	$900.92	$900.90	$900.90