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	$50.79	13.268%	$57.5288	$57.53	$57.55	$57.50
Purchase #2	$163.94	3.564%	$169.7828	$169.78	$169.80	$169.80
Purchase #3	$235.86	10.868%	$261.4933	$261.49	$261.50	$261.50
Purchase #4	$127.85	7.493%	$137.4298	$137.43	$137.45	$137.40
Purchase #5	$32.71	13.652%	$37.1756	$37.18	$37.20	$37.20
Purchase #6	$74.55	7.287%	$79.9825	$79.98	$80.00	$80.00
Purchase #7	$64.67	9.808%	$71.0128	$71.01	$71.00	$71.00
7 purchase totals =	$750.37		$814.4056	$814.40	$814.50	$814.40