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	$228.57	11.387%	$254.5973	$254.60	$254.60	$254.60
Purchase #2	$122.67	7.541%	$131.9205	$131.92	$131.90	$131.90
Purchase #3	$127.92	6.683%	$136.4689	$136.47	$136.45	$136.50
Purchase #4	$120.88	5.397%	$127.4039	$127.40	$127.40	$127.40
Purchase #5	$139.65	7.568%	$150.2187	$150.22	$150.20	$150.20
Purchase #6	$33.58	6.241%	$35.6757	$35.68	$35.70	$35.70
Purchase #7	$21.93	9.668%	$24.0502	$24.05	$24.05	$24.10
7 purchase totals =	$795.20		$860.3352	$860.34	$860.30	$860.40