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	$26.96	3.694%	$27.9559	$27.96	$27.95	$28.00
Purchase #2	$226.84	13.213%	$256.8124	$256.81	$256.80	$256.80
Purchase #3	$78.75	5.218%	$82.8592	$82.86	$82.85	$82.90
Purchase #4	$228.45	11.130%	$253.8765	$253.88	$253.90	$253.90
Purchase #5	$237.95	9.249%	$259.958	$259.96	$259.95	$260.00
Purchase #6	$47.66	10.593%	$52.7086	$52.71	$52.70	$52.70
Purchase #7	$52.58	13.701%	$59.784	$59.78	$59.80	$59.80
7 purchase totals =	$899.19		$993.9546	$993.96	$993.95	$994.10