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	$119.52	7.138%	$128.0513	$128.05	$128.05	$128.10
Purchase #2	$124.82	13.460%	$141.6208	$141.62	$141.60	$141.60
Purchase #3	$74.42	11.842%	$83.2328	$83.23	$83.25	$83.20
Purchase #4	$179.78	4.617%	$188.0804	$188.08	$188.10	$188.10
Purchase #5	$51.57	4.643%	$53.9644	$53.96	$53.95	$54.00
Purchase #6	$10.98	4.726%	$11.4989	$11.50	$11.50	$11.50
Purchase #7	$59.49	5.106%	$62.5276	$62.53	$62.55	$62.50
7 purchase totals =	$620.58		$668.9762	$668.97	$669.00	$669.00