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	$19.70	3.523%	$20.394	$20.39	$20.40	$20.40
Purchase #2	$119.55	6.818%	$127.7009	$127.70	$127.70	$127.70
Purchase #3	$161.72	7.572%	$173.9654	$173.97	$173.95	$174.00
Purchase #4	$236.54	4.319%	$246.7562	$246.76	$246.75	$246.80
Purchase #5	$71.66	9.491%	$78.4613	$78.46	$78.45	$78.50
Purchase #6	$113.86	9.436%	$124.6038	$124.60	$124.60	$124.60
Purchase #7	$31.34	13.587%	$35.5982	$35.60	$35.60	$35.60
7 purchase totals =	$754.37		$807.4798	$807.48	$807.45	$807.60