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	$241.28	8.392%	$261.5282	$261.53	$261.55	$261.50
Purchase #2	$151.75	3.199%	$156.6045	$156.60	$156.60	$156.60
Purchase #3	$237.35	10.678%	$262.6942	$262.69	$262.70	$262.70
Purchase #4	$127.31	8.130%	$137.6603	$137.66	$137.65	$137.70
Purchase #5	$70.51	12.553%	$79.3611	$79.36	$79.35	$79.40
Purchase #6	$41.48	9.778%	$45.5359	$45.54	$45.55	$45.50
Purchase #7	$246.60	4.132%	$256.7895	$256.79	$256.80	$256.80
7 purchase totals =	$1,116.28		$1,200.1737	$1,200.17	$1,200.20	$1,200.20