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	$209.99	11.844%	$234.8612	$234.86	$234.85	$234.90
Purchase #2	$152.57	13.707%	$173.4828	$173.48	$173.50	$173.50
Purchase #3	$123.81	7.777%	$133.4387	$133.44	$133.45	$133.40
Purchase #4	$177.54	12.422%	$199.594	$199.59	$199.60	$199.60
Purchase #5	$99.83	9.627%	$109.4406	$109.44	$109.45	$109.40
Purchase #6	$31.87	6.433%	$33.9202	$33.92	$33.90	$33.90
Purchase #7	$138.43	5.184%	$145.6062	$145.61	$145.60	$145.60
7 purchase totals =	$934.04		$1,030.3437	$1,030.34	$1,030.35	$1,030.30