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	$155.78	6.854%	$166.4572	$166.46	$166.45	$166.50
Purchase #2	$94.34	10.403%	$104.1542	$104.15	$104.15	$104.20
Purchase #3	$157.38	6.531%	$167.6585	$167.66	$167.65	$167.70
Purchase #4	$153.94	5.592%	$162.5483	$162.55	$162.55	$162.50
Purchase #5	$11.43	9.417%	$12.5064	$12.51	$12.50	$12.50
Purchase #6	$229.77	13.463%	$260.7039	$260.70	$260.70	$260.70
Purchase #7	$76.77	9.294%	$83.905	$83.91	$83.90	$83.90
7 purchase totals =	$879.41		$957.9335	$957.94	$957.90	$958.00