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	$71.25	12.410%	$80.0921	$80.09	$80.10	$80.10
Purchase #2	$104.89	12.244%	$117.7327	$117.73	$117.75	$117.70
Purchase #3	$98.58	13.202%	$111.5945	$111.59	$111.60	$111.60
Purchase #4	$206.86	8.563%	$224.5734	$224.57	$224.55	$224.60
Purchase #5	$136.55	13.665%	$155.2096	$155.21	$155.20	$155.20
Purchase #6	$108.71	9.422%	$118.9527	$118.95	$118.95	$119.00
Purchase #7	$43.92	3.327%	$45.3812	$45.38	$45.40	$45.40
7 purchase totals =	$770.76		$853.5362	$853.52	$853.55	$853.60