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	$136.50	11.307%	$151.9341	$151.93	$151.95	$151.90
Purchase #2	$84.86	6.743%	$90.5821	$90.58	$90.60	$90.60
Purchase #3	$138.50	9.469%	$151.6146	$151.61	$151.60	$151.60
Purchase #4	$245.30	7.170%	$262.888	$262.89	$262.90	$262.90
Purchase #5	$40.37	6.417%	$42.9605	$42.96	$42.95	$43.00
Purchase #6	$78.30	12.167%	$87.8268	$87.83	$87.85	$87.80
Purchase #7	$192.72	10.450%	$212.8592	$212.86	$212.85	$212.90
7 purchase totals =	$916.55		$1,000.6653	$1,000.66	$1,000.70	$1,000.70