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	$197.88	5.217%	$208.2034	$208.20	$208.20	$208.20
Purchase #2	$112.88	3.492%	$116.8218	$116.82	$116.80	$116.80
Purchase #3	$52.90	12.801%	$59.6717	$59.67	$59.65	$59.70
Purchase #4	$40.63	8.136%	$43.9357	$43.94	$43.95	$43.90
Purchase #5	$78.53	10.186%	$86.5291	$86.53	$86.55	$86.50
Purchase #6	$103.99	10.177%	$114.5731	$114.57	$114.55	$114.60
Purchase #7	$134.25	12.373%	$150.8608	$150.86	$150.85	$150.90
7 purchase totals =	$721.06		$780.5956	$780.59	$780.55	$780.60