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	$224.28	13.785%	$255.197	$255.20	$255.20	$255.20
Purchase #2	$136.69	5.873%	$144.7178	$144.72	$144.70	$144.70
Purchase #3	$167.37	10.844%	$185.5196	$185.52	$185.50	$185.50
Purchase #4	$143.43	3.719%	$148.7642	$148.76	$148.75	$148.80
Purchase #5	$200.56	9.483%	$219.5791	$219.58	$219.60	$219.60
Purchase #6	$242.35	12.813%	$273.4023	$273.40	$273.40	$273.40
Purchase #7	$121.37	13.365%	$137.5911	$137.59	$137.60	$137.60
7 purchase totals =	$1,236.05		$1,364.7711	$1,364.77	$1,364.75	$1,364.80