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	$140.86	6.549%	$150.0849	$150.08	$150.10	$150.10
Purchase #2	$112.30	9.806%	$123.3121	$123.31	$123.30	$123.30
Purchase #3	$175.71	9.757%	$192.854	$192.85	$192.85	$192.90
Purchase #4	$88.52	3.480%	$91.6005	$91.60	$91.60	$91.60
Purchase #5	$112.80	13.874%	$128.4499	$128.45	$128.45	$128.40
Purchase #6	$116.77	6.252%	$124.0705	$124.07	$124.05	$124.10
Purchase #7	$123.29	6.297%	$131.0536	$131.05	$131.05	$131.10
7 purchase totals =	$870.25		$941.4255	$941.41	$941.40	$941.50