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	$250.28	3.146%	$258.1538	$258.15	$258.15	$258.20
Purchase #2	$222.42	5.575%	$234.8199	$234.82	$234.80	$234.80
Purchase #3	$86.58	9.297%	$94.6293	$94.63	$94.65	$94.60
Purchase #4	$112.55	9.856%	$123.6429	$123.64	$123.65	$123.60
Purchase #5	$247.66	8.772%	$269.3847	$269.38	$269.40	$269.40
Purchase #6	$16.63	9.167%	$18.1545	$18.15	$18.15	$18.20
Purchase #7	$35.55	13.443%	$40.329	$40.33	$40.35	$40.30
7 purchase totals =	$971.67		$1,039.1141	$1,039.10	$1,039.15	$1,039.10