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	$217.37	10.596%	$240.4025	$240.40	$240.40	$240.40
Purchase #2	$21.38	12.594%	$24.0726	$24.07	$24.05	$24.10
Purchase #3	$7.29	8.168%	$7.8854	$7.89	$7.90	$7.90
Purchase #4	$226.93	3.349%	$234.5299	$234.53	$234.55	$234.50
Purchase #5	$213.31	4.511%	$222.9324	$222.93	$222.95	$222.90
Purchase #6	$56.28	11.708%	$62.8693	$62.87	$62.85	$62.90
Purchase #7	$43.61	3.549%	$45.1577	$45.16	$45.15	$45.20
7 purchase totals =	$786.17		$837.8498	$837.85	$837.85	$837.90