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	$200.82	10.263%	$221.4302	$221.43	$221.45	$221.40
Purchase #2	$143.74	5.106%	$151.0794	$151.08	$151.10	$151.10
Purchase #3	$169.61	5.444%	$178.8436	$178.84	$178.85	$178.80
Purchase #4	$38.76	11.509%	$43.2209	$43.22	$43.20	$43.20
Purchase #5	$100.30	12.230%	$112.5667	$112.57	$112.55	$112.60
Purchase #6	$77.34	5.680%	$81.7329	$81.73	$81.75	$81.70
Purchase #7	$18.31	5.856%	$19.3822	$19.38	$19.40	$19.40
7 purchase totals =	$748.88		$808.2559	$808.25	$808.30	$808.20