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	$243.88	5.781%	$257.9787	$257.98	$258.00	$258.00
Purchase #2	$64.39	8.517%	$69.8741	$69.87	$69.85	$69.90
Purchase #3	$38.51	8.734%	$41.8735	$41.87	$41.85	$41.90
Purchase #4	$65.86	10.592%	$72.8359	$72.84	$72.85	$72.80
Purchase #5	$112.49	5.387%	$118.5498	$118.55	$118.55	$118.50
Purchase #6	$17.90	5.493%	$18.8832	$18.88	$18.90	$18.90
Purchase #7	$138.78	8.267%	$150.2529	$150.25	$150.25	$150.30
7 purchase totals =	$681.81		$730.2481	$730.24	$730.25	$730.30