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	$39.51	10.648%	$43.717	$43.72	$43.70	$43.70
Purchase #2	$212.59	4.605%	$222.3798	$222.38	$222.40	$222.40
Purchase #3	$32.86	6.172%	$34.8881	$34.89	$34.90	$34.90
Purchase #4	$45.90	12.822%	$51.7853	$51.79	$51.80	$51.80
Purchase #5	$70.52	10.567%	$77.9718	$77.97	$77.95	$78.00
Purchase #6	$8.86	12.599%	$9.9763	$9.98	$10.00	$10.00
Purchase #7	$175.55	7.649%	$188.9778	$188.98	$189.00	$189.00
7 purchase totals =	$585.79		$629.6961	$629.71	$629.75	$629.80