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	$33.48	7.750%	$36.0747	$36.07	$36.05	$36.10
Purchase #2	$218.39	12.246%	$245.134	$245.13	$245.15	$245.10
Purchase #3	$107.31	8.379%	$116.3015	$116.30	$116.30	$116.30
Purchase #4	$40.30	11.369%	$44.8817	$44.88	$44.90	$44.90
Purchase #5	$134.82	11.514%	$150.3432	$150.34	$150.35	$150.30
Purchase #6	$38.54	11.308%	$42.8981	$42.90	$42.90	$42.90
Purchase #7	$227.87	11.657%	$254.4328	$254.43	$254.45	$254.40
7 purchase totals =	$800.71		$890.0660	$890.05	$890.10	$890.00