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	$95.92	8.387%	$103.9648	$103.96	$103.95	$104.00
Purchase #2	$38.67	4.667%	$40.4747	$40.47	$40.45	$40.50
Purchase #3	$64.81	12.332%	$72.8024	$72.80	$72.80	$72.80
Purchase #4	$5.57	6.717%	$5.9441	$5.94	$5.95	$5.90
Purchase #5	$124.57	6.353%	$132.4839	$132.48	$132.50	$132.50
Purchase #6	$152.87	4.374%	$159.5565	$159.56	$159.55	$159.60
Purchase #7	$64.64	10.460%	$71.4013	$71.40	$71.40	$71.40
7 purchase totals =	$547.05		$586.6277	$586.61	$586.60	$586.70