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	$27.71	13.636%	$31.4885	$31.49	$31.50	$31.50
Purchase #2	$161.37	7.610%	$173.6503	$173.65	$173.65	$173.70
Purchase #3	$245.46	4.109%	$255.546	$255.55	$255.55	$255.50
Purchase #4	$45.80	4.164%	$47.7071	$47.71	$47.70	$47.70
Purchase #5	$87.39	10.534%	$96.5957	$96.60	$96.60	$96.60
Purchase #6	$89.40	6.819%	$95.4962	$95.50	$95.50	$95.50
Purchase #7	$208.25	7.633%	$224.1457	$224.15	$224.15	$224.10
7 purchase totals =	$865.38		$924.6295	$924.65	$924.65	$924.60