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	$44.90	6.527%	$47.8306	$47.83	$47.85	$47.80
Purchase #2	$143.93	6.644%	$153.4927	$153.49	$153.50	$153.50
Purchase #3	$46.43	4.719%	$48.621	$48.62	$48.60	$48.60
Purchase #4	$39.79	11.402%	$44.3269	$44.33	$44.35	$44.30
Purchase #5	$43.77	6.191%	$46.4798	$46.48	$46.50	$46.50
Purchase #6	$104.36	3.380%	$107.8874	$107.89	$107.90	$107.90
Purchase #7	$54.89	8.109%	$59.341	$59.34	$59.35	$59.30
7 purchase totals =	$478.07		$507.9794	$507.98	$508.05	$507.90