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	$127.92	9.346%	$139.8754	$139.88	$139.90	$139.90
Purchase #2	$31.46	13.336%	$35.6555	$35.66	$35.65	$35.70
Purchase #3	$14.48	11.102%	$16.0876	$16.09	$16.10	$16.10
Purchase #4	$157.96	9.193%	$172.4813	$172.48	$172.50	$172.50
Purchase #5	$186.29	5.556%	$196.6403	$196.64	$196.65	$196.60
Purchase #6	$70.60	10.769%	$78.2029	$78.20	$78.20	$78.20
Purchase #7	$139.38	13.431%	$158.1001	$158.10	$158.10	$158.10
7 purchase totals =	$728.09		$797.0431	$797.05	$797.10	$797.10