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	$238.64	9.142%	$260.4565	$260.46	$260.45	$260.50
Purchase #2	$187.27	10.461%	$206.8603	$206.86	$206.85	$206.90
Purchase #3	$222.40	12.585%	$250.389	$250.39	$250.40	$250.40
Purchase #4	$186.28	10.368%	$205.5935	$205.59	$205.60	$205.60
Purchase #5	$35.53	5.523%	$37.4923	$37.49	$37.50	$37.50
Purchase #6	$182.46	4.232%	$190.1817	$190.18	$190.20	$190.20
Purchase #7	$179.27	11.594%	$200.0546	$200.05	$200.05	$200.10
7 purchase totals =	$1,231.85		$1,351.0279	$1,351.02	$1,351.05	$1,351.20