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	$127.43	7.514%	$137.0051	$137.01	$137.00	$137.00
Purchase #2	$250.46	8.382%	$271.4536	$271.45	$271.45	$271.50
Purchase #3	$114.96	13.690%	$130.698	$130.70	$130.70	$130.70
Purchase #4	$65.47	10.813%	$72.5493	$72.55	$72.55	$72.50
Purchase #5	$116.64	8.712%	$126.8017	$126.80	$126.80	$126.80
Purchase #6	$227.38	12.226%	$255.1795	$255.18	$255.20	$255.20
Purchase #7	$225.80	8.268%	$244.4691	$244.47	$244.45	$244.50
7 purchase totals =	$1,128.14		$1,238.1563	$1,238.16	$1,238.15	$1,238.20