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	$134.35	7.629%	$144.5996	$144.60	$144.60	$144.60
Purchase #2	$100.91	8.412%	$109.3985	$109.40	$109.40	$109.40
Purchase #3	$51.58	7.504%	$55.4506	$55.45	$55.45	$55.50
Purchase #4	$33.65	5.761%	$35.5886	$35.59	$35.60	$35.60
Purchase #5	$195.63	4.545%	$204.5214	$204.52	$204.50	$204.50
Purchase #6	$14.42	3.355%	$14.9038	$14.90	$14.90	$14.90
Purchase #7	$26.39	11.284%	$29.3678	$29.37	$29.35	$29.40
7 purchase totals =	$556.93		$593.8303	$593.83	$593.80	$593.90