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	$122.38	13.834%	$139.31	$139.31	$139.30	$139.30
Purchase #2	$237.60	11.323%	$264.5034	$264.50	$264.50	$264.50
Purchase #3	$189.93	3.262%	$196.1255	$196.13	$196.15	$196.10
Purchase #4	$237.30	5.398%	$250.1095	$250.11	$250.10	$250.10
Purchase #5	$100.41	10.564%	$111.0173	$111.02	$111.00	$111.00
Purchase #6	$134.43	3.413%	$139.0181	$139.02	$139.00	$139.00
Purchase #7	$126.82	9.598%	$138.9922	$138.99	$139.00	$139.00
7 purchase totals =	$1,148.87		$1,239.0760	$1,239.08	$1,239.05	$1,239.00