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	$81.43	9.731%	$89.354	$89.35	$89.35	$89.40
Purchase #2	$108.85	13.203%	$123.2215	$123.22	$123.20	$123.20
Purchase #3	$198.34	3.843%	$205.9622	$205.96	$205.95	$206.00
Purchase #4	$43.68	4.615%	$45.6958	$45.70	$45.70	$45.70
Purchase #5	$141.73	8.524%	$153.8111	$153.81	$153.80	$153.80
Purchase #6	$249.91	12.265%	$280.5615	$280.56	$280.55	$280.60
Purchase #7	$220.91	9.154%	$241.1321	$241.13	$241.15	$241.10
7 purchase totals =	$1,044.85		$1,139.7382	$1,139.73	$1,139.70	$1,139.80