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	$62.56	12.481%	$70.3681	$70.37	$70.35	$70.40
Purchase #2	$53.84	4.410%	$56.2143	$56.21	$56.20	$56.20
Purchase #3	$14.70	7.527%	$15.8065	$15.81	$15.80	$15.80
Purchase #4	$195.52	5.591%	$206.4515	$206.45	$206.45	$206.50
Purchase #5	$90.93	10.354%	$100.3449	$100.34	$100.35	$100.30
Purchase #6	$138.29	6.655%	$147.4932	$147.49	$147.50	$147.50
Purchase #7	$40.82	11.632%	$45.5682	$45.57	$45.55	$45.60
7 purchase totals =	$596.66		$642.2467	$642.24	$642.20	$642.30