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	$50.65	3.371%	$52.3574	$52.36	$52.35	$52.40
Purchase #2	$140.92	7.640%	$151.6863	$151.69	$151.70	$151.70
Purchase #3	$119.77	6.409%	$127.4461	$127.45	$127.45	$127.40
Purchase #4	$42.94	4.176%	$44.7332	$44.73	$44.75	$44.70
Purchase #5	$117.46	5.432%	$123.8404	$123.84	$123.85	$123.80
Purchase #6	$176.29	6.244%	$187.2975	$187.30	$187.30	$187.30
Purchase #7	$166.39	8.298%	$180.197	$180.20	$180.20	$180.20
7 purchase totals =	$814.42		$867.5579	$867.57	$867.60	$867.50