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	$138.38	11.452%	$154.2273	$154.23	$154.25	$154.20
Purchase #2	$178.83	4.425%	$186.7432	$186.74	$186.75	$186.70
Purchase #3	$118.92	12.541%	$133.8338	$133.83	$133.85	$133.80
Purchase #4	$52.66	13.724%	$59.8871	$59.89	$59.90	$59.90
Purchase #5	$233.63	13.407%	$264.9528	$264.95	$264.95	$265.00
Purchase #6	$117.59	6.222%	$124.9064	$124.91	$124.90	$124.90
Purchase #7	$38.76	13.134%	$43.8507	$43.85	$43.85	$43.90
7 purchase totals =	$878.77		$968.4013	$968.40	$968.45	$968.40