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	$51.86	8.507%	$56.2717	$56.27	$56.25	$56.30
Purchase #2	$7.91	4.387%	$8.257	$8.26	$8.25	$8.30
Purchase #3	$54.51	12.661%	$61.4115	$61.41	$61.40	$61.40
Purchase #4	$12.43	7.778%	$13.3968	$13.40	$13.40	$13.40
Purchase #5	$92.86	8.251%	$100.5219	$100.52	$100.50	$100.50
Purchase #6	$162.58	10.830%	$180.1874	$180.19	$180.20	$180.20
Purchase #7	$79.72	9.678%	$87.4353	$87.44	$87.45	$87.40
7 purchase totals =	$461.87		$507.4816	$507.49	$507.45	$507.50