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	$113.43	13.160%	$128.3574	$128.36	$128.35	$128.40
Purchase #2	$172.60	7.153%	$184.9461	$184.95	$184.95	$184.90
Purchase #3	$126.60	10.257%	$139.5854	$139.59	$139.60	$139.60
Purchase #4	$83.46	3.604%	$86.4679	$86.47	$86.45	$86.50
Purchase #5	$186.48	10.860%	$206.7317	$206.73	$206.75	$206.70
Purchase #6	$138.69	7.265%	$148.7658	$148.77	$148.75	$148.80
Purchase #7	$91.91	8.431%	$99.6589	$99.66	$99.65	$99.70
7 purchase totals =	$913.17		$994.5132	$994.53	$994.50	$994.60