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	$224.57	13.749%	$255.4461	$255.45	$255.45	$255.40
Purchase #2	$106.54	6.862%	$113.8508	$113.85	$113.85	$113.90
Purchase #3	$159.29	11.700%	$177.9269	$177.93	$177.95	$177.90
Purchase #4	$40.74	5.452%	$42.9611	$42.96	$42.95	$43.00
Purchase #5	$183.33	12.328%	$205.9309	$205.93	$205.95	$205.90
Purchase #6	$20.62	3.426%	$21.3264	$21.33	$21.35	$21.30
Purchase #7	$241.35	3.735%	$250.3644	$250.36	$250.35	$250.40
7 purchase totals =	$976.44		$1,067.8066	$1,067.81	$1,067.85	$1,067.80