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	$241.90	12.697%	$272.614	$272.61	$272.60	$272.60
Purchase #2	$226.44	13.242%	$256.4252	$256.43	$256.45	$256.40
Purchase #3	$250.81	4.801%	$262.8514	$262.85	$262.85	$262.90
Purchase #4	$40.51	13.264%	$45.8832	$45.88	$45.90	$45.90
Purchase #5	$93.68	13.689%	$106.5039	$106.50	$106.50	$106.50
Purchase #6	$44.31	3.166%	$45.7129	$45.71	$45.70	$45.70
Purchase #7	$137.27	8.546%	$149.0011	$149.00	$149.00	$149.00
7 purchase totals =	$1,034.92		$1,138.9917	$1,138.98	$1,139.00	$1,139.00