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	$74.35	5.871%	$78.7151	$78.72	$78.70	$78.70
Purchase #2	$40.37	8.405%	$43.7631	$43.76	$43.75	$43.80
Purchase #3	$15.61	4.437%	$16.3026	$16.30	$16.30	$16.30
Purchase #4	$204.85	5.706%	$216.5387	$216.54	$216.55	$216.50
Purchase #5	$142.83	7.722%	$153.8593	$153.86	$153.85	$153.90
Purchase #6	$42.47	13.729%	$48.3007	$48.30	$48.30	$48.30
Purchase #7	$239.74	10.622%	$265.2052	$265.21	$265.20	$265.20
7 purchase totals =	$760.22		$822.6847	$822.69	$822.65	$822.70