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	$139.26	11.816%	$155.715	$155.72	$155.70	$155.70
Purchase #2	$249.80	9.193%	$272.7641	$272.76	$272.75	$272.80
Purchase #3	$204.86	4.757%	$214.6052	$214.61	$214.60	$214.60
Purchase #4	$37.40	9.366%	$40.9029	$40.90	$40.90	$40.90
Purchase #5	$90.84	9.577%	$99.5397	$99.54	$99.55	$99.50
Purchase #6	$218.25	13.811%	$248.3925	$248.39	$248.40	$248.40
Purchase #7	$9.86	5.796%	$10.4315	$10.43	$10.45	$10.40
7 purchase totals =	$950.27		$1,042.3509	$1,042.35	$1,042.35	$1,042.30