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	$132.46	5.323%	$139.5108	$139.51	$139.50	$139.50
Purchase #2	$225.90	13.749%	$256.959	$256.96	$256.95	$257.00
Purchase #3	$9.42	10.161%	$10.3772	$10.38	$10.40	$10.40
Purchase #4	$76.49	3.177%	$78.9201	$78.92	$78.90	$78.90
Purchase #5	$30.27	4.704%	$31.6939	$31.69	$31.70	$31.70
Purchase #6	$176.59	5.234%	$185.8327	$185.83	$185.85	$185.80
Purchase #7	$33.31	7.649%	$35.8579	$35.86	$35.85	$35.90
7 purchase totals =	$684.44		$739.1516	$739.15	$739.15	$739.20