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	$16.28	3.532%	$16.855	$16.86	$16.85	$16.90
Purchase #2	$236.61	12.266%	$265.6326	$265.63	$265.65	$265.60
Purchase #3	$107.77	5.369%	$113.5562	$113.56	$113.55	$113.60
Purchase #4	$170.51	5.467%	$179.8318	$179.83	$179.85	$179.80
Purchase #5	$46.52	12.858%	$52.5015	$52.50	$52.50	$52.50
Purchase #6	$220.39	13.630%	$250.4292	$250.43	$250.45	$250.40
Purchase #7	$80.53	12.853%	$90.8805	$90.88	$90.90	$90.90
7 purchase totals =	$878.61		$969.6868	$969.69	$969.75	$969.70