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	$111.31	4.562%	$116.388	$116.39	$116.40	$116.40
Purchase #2	$34.93	10.686%	$38.6626	$38.66	$38.65	$38.70
Purchase #3	$211.79	12.652%	$238.5857	$238.59	$238.60	$238.60
Purchase #4	$69.50	10.329%	$76.6787	$76.68	$76.70	$76.70
Purchase #5	$198.34	12.239%	$222.6148	$222.61	$222.60	$222.60
Purchase #6	$38.82	4.762%	$40.6686	$40.67	$40.65	$40.70
Purchase #7	$86.38	3.282%	$89.215	$89.22	$89.20	$89.20
7 purchase totals =	$751.07		$822.8134	$822.82	$822.80	$822.90