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	$126.93	10.329%	$140.0406	$140.04	$140.05	$140.00
Purchase #2	$34.29	5.348%	$36.1238	$36.12	$36.10	$36.10
Purchase #3	$43.46	5.157%	$45.7012	$45.70	$45.70	$45.70
Purchase #4	$195.51	6.547%	$208.31	$208.31	$208.30	$208.30
Purchase #5	$76.54	3.108%	$78.9189	$78.92	$78.90	$78.90
Purchase #6	$228.49	5.624%	$241.3403	$241.34	$241.35	$241.30
Purchase #7	$95.68	3.486%	$99.0154	$99.02	$99.00	$99.00
7 purchase totals =	$800.90		$849.4502	$849.45	$849.40	$849.30