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	$250.72	11.403%	$279.3096	$279.31	$279.30	$279.30
Purchase #2	$136.30	13.666%	$154.9268	$154.93	$154.95	$154.90
Purchase #3	$83.54	8.299%	$90.473	$90.47	$90.45	$90.50
Purchase #4	$92.25	6.334%	$98.0931	$98.09	$98.10	$98.10
Purchase #5	$144.84	5.569%	$152.9061	$152.91	$152.90	$152.90
Purchase #6	$176.40	3.824%	$183.1455	$183.15	$183.15	$183.10
Purchase #7	$71.78	3.466%	$74.2679	$74.27	$74.25	$74.30
7 purchase totals =	$955.83		$1,033.1220	$1,033.13	$1,033.10	$1,033.10