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	$211.68	12.457%	$238.049	$238.05	$238.05	$238.00
Purchase #2	$145.25	7.653%	$156.366	$156.37	$156.35	$156.40
Purchase #3	$73.52	10.823%	$81.4771	$81.48	$81.50	$81.50
Purchase #4	$179.67	11.523%	$200.3734	$200.37	$200.35	$200.40
Purchase #5	$116.75	4.173%	$121.622	$121.62	$121.60	$121.60
Purchase #6	$43.41	12.329%	$48.762	$48.76	$48.75	$48.80
Purchase #7	$86.34	4.502%	$90.227	$90.23	$90.25	$90.20
7 purchase totals =	$856.62		$936.8765	$936.88	$936.85	$936.90