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	$179.46	13.599%	$203.8648	$203.86	$203.85	$203.90
Purchase #2	$201.92	9.240%	$220.5774	$220.58	$220.60	$220.60
Purchase #3	$71.57	10.292%	$78.936	$78.94	$78.95	$78.90
Purchase #4	$42.39	3.105%	$43.7062	$43.71	$43.70	$43.70
Purchase #5	$152.39	3.869%	$158.286	$158.29	$158.30	$158.30
Purchase #6	$166.77	5.588%	$176.0891	$176.09	$176.10	$176.10
Purchase #7	$84.51	9.279%	$92.3517	$92.35	$92.35	$92.40
7 purchase totals =	$899.01		$973.8112	$973.82	$973.85	$973.90