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	$131.78	6.230%	$139.9899	$139.99	$140.00	$140.00
Purchase #2	$189.52	3.628%	$196.3958	$196.40	$196.40	$196.40
Purchase #3	$43.88	8.665%	$47.6822	$47.68	$47.70	$47.70
Purchase #4	$74.54	5.155%	$78.3825	$78.38	$78.40	$78.40
Purchase #5	$61.47	6.277%	$65.3285	$65.33	$65.35	$65.30
Purchase #6	$42.98	6.647%	$45.8369	$45.84	$45.85	$45.80
Purchase #7	$65.83	10.169%	$72.5243	$72.52	$72.50	$72.50
7 purchase totals =	$610.00		$646.1401	$646.14	$646.20	$646.10