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	$34.93	13.670%	$39.7049	$39.70	$39.70	$39.70
Purchase #2	$72.90	7.606%	$78.4448	$78.44	$78.45	$78.40
Purchase #3	$98.28	13.458%	$111.5065	$111.51	$111.50	$111.50
Purchase #4	$183.79	8.292%	$199.0299	$199.03	$199.05	$199.00
Purchase #5	$179.47	6.178%	$190.5577	$190.56	$190.55	$190.60
Purchase #6	$161.36	3.854%	$167.5788	$167.58	$167.60	$167.60
Purchase #7	$193.98	12.293%	$217.826	$217.83	$217.85	$217.80
7 purchase totals =	$924.71		$1,004.6486	$1,004.65	$1,004.70	$1,004.60