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	$65.93	6.732%	$70.3684	$70.37	$70.35	$70.40
Purchase #2	$41.64	7.770%	$44.8754	$44.88	$44.90	$44.90
Purchase #3	$235.48	12.396%	$264.6701	$264.67	$264.65	$264.70
Purchase #4	$43.60	4.631%	$45.6191	$45.62	$45.60	$45.60
Purchase #5	$233.45	10.758%	$258.5646	$258.56	$258.55	$258.60
Purchase #6	$19.80	3.858%	$20.5639	$20.56	$20.55	$20.60
Purchase #7	$51.78	5.567%	$54.6626	$54.66	$54.65	$54.70
7 purchase totals =	$691.68		$759.3241	$759.32	$759.25	$759.50