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	$172.31	4.175%	$179.5039	$179.50	$179.50	$179.50
Purchase #2	$164.38	7.469%	$176.6575	$176.66	$176.65	$176.70
Purchase #3	$208.86	11.226%	$232.3066	$232.31	$232.30	$232.30
Purchase #4	$164.82	8.113%	$178.1918	$178.19	$178.20	$178.20
Purchase #5	$227.50	9.672%	$249.5038	$249.50	$249.50	$249.50
Purchase #6	$38.49	10.649%	$42.5888	$42.59	$42.60	$42.60
Purchase #7	$36.98	3.498%	$38.2736	$38.27	$38.25	$38.30
7 purchase totals =	$1,013.34		$1,097.0260	$1,097.02	$1,097.00	$1,097.10