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	$134.59	3.717%	$139.5927	$139.59	$139.60	$139.60
Purchase #2	$45.27	11.737%	$50.5833	$50.58	$50.60	$50.60
Purchase #3	$170.59	8.624%	$185.3017	$185.30	$185.30	$185.30
Purchase #4	$112.45	11.629%	$125.5268	$125.53	$125.55	$125.50
Purchase #5	$117.34	3.757%	$121.7485	$121.75	$121.75	$121.70
Purchase #6	$154.34	12.281%	$173.2945	$173.29	$173.30	$173.30
Purchase #7	$59.32	9.339%	$64.8599	$64.86	$64.85	$64.90
7 purchase totals =	$793.90		$860.9074	$860.90	$860.95	$860.90