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	$242.40	7.375%	$260.277	$260.28	$260.30	$260.30
Purchase #2	$90.83	13.785%	$103.3509	$103.35	$103.35	$103.40
Purchase #3	$139.61	11.788%	$156.0672	$156.07	$156.05	$156.10
Purchase #4	$73.76	9.830%	$81.0106	$81.01	$81.00	$81.00
Purchase #5	$198.96	4.839%	$208.5877	$208.59	$208.60	$208.60
Purchase #6	$151.42	8.581%	$164.4134	$164.41	$164.40	$164.40
Purchase #7	$250.81	13.554%	$284.8048	$284.80	$284.80	$284.80
7 purchase totals =	$1,147.79		$1,258.5116	$1,258.51	$1,258.50	$1,258.60