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	$163.26	13.229%	$184.8577	$184.86	$184.85	$184.90
Purchase #2	$217.80	3.682%	$225.8194	$225.82	$225.80	$225.80
Purchase #3	$224.34	6.796%	$239.5861	$239.59	$239.60	$239.60
Purchase #4	$37.71	10.704%	$41.7465	$41.75	$41.75	$41.70
Purchase #5	$150.64	5.810%	$159.3922	$159.39	$159.40	$159.40
Purchase #6	$78.33	5.343%	$82.5152	$82.52	$82.50	$82.50
Purchase #7	$43.53	7.810%	$46.9297	$46.93	$46.95	$46.90
7 purchase totals =	$915.61		$980.8468	$980.86	$980.85	$980.80