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	$136.77	5.798%	$144.6999	$144.70	$144.70	$144.70
Purchase #2	$223.94	8.481%	$242.9324	$242.93	$242.95	$242.90
Purchase #3	$144.57	5.258%	$152.1715	$152.17	$152.15	$152.20
Purchase #4	$52.82	3.357%	$54.5932	$54.59	$54.60	$54.60
Purchase #5	$100.99	3.484%	$104.5085	$104.51	$104.50	$104.50
Purchase #6	$58.78	4.153%	$61.2211	$61.22	$61.20	$61.20
Purchase #7	$218.31	9.159%	$238.305	$238.31	$238.30	$238.30
7 purchase totals =	$936.18		$998.4316	$998.43	$998.40	$998.40