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	$135.34	5.698%	$143.0517	$143.05	$143.05	$143.10
Purchase #2	$52.40	6.108%	$55.6006	$55.60	$55.60	$55.60
Purchase #3	$207.80	9.246%	$227.0132	$227.01	$227.00	$227.00
Purchase #4	$248.91	12.342%	$279.6305	$279.63	$279.65	$279.60
Purchase #5	$86.37	5.298%	$90.9459	$90.95	$90.95	$90.90
Purchase #6	$49.46	7.786%	$53.311	$53.31	$53.30	$53.30
Purchase #7	$10.36	10.613%	$11.4595	$11.46	$11.45	$11.50
7 purchase totals =	$790.64		$861.0124	$861.01	$861.00	$861.00