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	$229.42	7.264%	$246.0851	$246.09	$246.10	$246.10
Purchase #2	$161.28	3.217%	$166.4684	$166.47	$166.45	$166.50
Purchase #3	$168.83	9.247%	$184.4417	$184.44	$184.45	$184.40
Purchase #4	$104.59	13.346%	$118.5486	$118.55	$118.55	$118.50
Purchase #5	$103.86	5.854%	$109.94	$109.94	$109.95	$109.90
Purchase #6	$26.46	3.745%	$27.4509	$27.45	$27.45	$27.50
Purchase #7	$92.67	12.862%	$104.5892	$104.59	$104.60	$104.60
7 purchase totals =	$887.11		$957.5239	$957.53	$957.55	$957.50