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	$244.99	13.613%	$278.3405	$278.34	$278.35	$278.30
Purchase #2	$160.70	11.676%	$179.4633	$179.46	$179.45	$179.50
Purchase #3	$127.36	5.692%	$134.6093	$134.61	$134.60	$134.60
Purchase #4	$143.58	5.495%	$151.4697	$151.47	$151.45	$151.50
Purchase #5	$84.71	7.380%	$90.9616	$90.96	$90.95	$91.00
Purchase #6	$34.90	3.172%	$36.007	$36.01	$36.00	$36.00
Purchase #7	$211.40	12.617%	$238.0723	$238.07	$238.05	$238.10
7 purchase totals =	$1,007.64		$1,108.9237	$1,108.92	$1,108.85	$1,109.00