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	$233.44	13.651%	$265.3069	$265.31	$265.30	$265.30
Purchase #2	$193.39	6.311%	$205.5948	$205.59	$205.60	$205.60
Purchase #3	$83.79	7.747%	$90.2812	$90.28	$90.30	$90.30
Purchase #4	$86.83	3.476%	$89.8482	$89.85	$89.85	$89.80
Purchase #5	$176.93	5.185%	$186.1038	$186.10	$186.10	$186.10
Purchase #6	$73.52	7.172%	$78.7929	$78.79	$78.80	$78.80
Purchase #7	$195.94	9.301%	$214.1644	$214.16	$214.15	$214.20
7 purchase totals =	$1,043.84		$1,130.0922	$1,130.08	$1,130.10	$1,130.10