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	$133.41	4.315%	$139.1666	$139.17	$139.15	$139.20
Purchase #2	$70.40	11.614%	$78.5763	$78.58	$78.60	$78.60
Purchase #3	$165.42	13.718%	$188.1123	$188.11	$188.10	$188.10
Purchase #4	$127.88	8.309%	$138.5055	$138.51	$138.50	$138.50
Purchase #5	$94.85	9.268%	$103.6407	$103.64	$103.65	$103.60
Purchase #6	$181.64	6.218%	$192.9344	$192.93	$192.95	$192.90
Purchase #7	$90.34	11.240%	$100.4942	$100.49	$100.50	$100.50
7 purchase totals =	$863.94		$941.4300	$941.43	$941.45	$941.40