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	$227.45	12.456%	$255.7812	$255.78	$255.80	$255.80
Purchase #2	$63.82	12.493%	$71.793	$71.79	$71.80	$71.80
Purchase #3	$97.27	3.150%	$100.334	$100.33	$100.35	$100.30
Purchase #4	$90.70	13.756%	$103.1767	$103.18	$103.20	$103.20
Purchase #5	$109.99	10.219%	$121.2299	$121.23	$121.25	$121.20
Purchase #6	$101.86	11.222%	$113.2907	$113.29	$113.30	$113.30
Purchase #7	$221.51	4.678%	$231.8722	$231.87	$231.85	$231.90
7 purchase totals =	$912.60		$997.4777	$997.47	$997.55	$997.50