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	$18.78	3.827%	$19.4987	$19.50	$19.50	$19.50
Purchase #2	$111.76	5.765%	$118.203	$118.20	$118.20	$118.20
Purchase #3	$136.37	12.539%	$153.4694	$153.47	$153.45	$153.50
Purchase #4	$36.98	9.546%	$40.5101	$40.51	$40.50	$40.50
Purchase #5	$97.90	5.271%	$103.0603	$103.06	$103.05	$103.10
Purchase #6	$12.92	7.854%	$13.9347	$13.93	$13.95	$13.90
Purchase #7	$28.96	12.382%	$32.5458	$32.55	$32.55	$32.50
7 purchase totals =	$443.67		$481.2220	$481.22	$481.20	$481.20