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	$142.58	6.182%	$151.3943	$151.39	$151.40	$151.40
Purchase #2	$205.33	12.630%	$231.2632	$231.26	$231.25	$231.30
Purchase #3	$56.53	4.643%	$59.1547	$59.15	$59.15	$59.20
Purchase #4	$40.86	7.586%	$43.9596	$43.96	$43.95	$44.00
Purchase #5	$21.42	11.581%	$23.9007	$23.90	$23.90	$23.90
Purchase #6	$147.77	12.509%	$166.2545	$166.25	$166.25	$166.30
Purchase #7	$81.91	9.575%	$89.7529	$89.75	$89.75	$89.80
7 purchase totals =	$696.40		$765.6799	$765.66	$765.65	$765.90