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	$225.37	8.409%	$244.3214	$244.32	$244.30	$244.30
Purchase #2	$160.96	7.661%	$173.2911	$173.29	$173.30	$173.30
Purchase #3	$245.90	13.155%	$278.2481	$278.25	$278.25	$278.20
Purchase #4	$99.35	12.102%	$111.3733	$111.37	$111.35	$111.40
Purchase #5	$117.31	3.220%	$121.0874	$121.09	$121.10	$121.10
Purchase #6	$38.42	3.146%	$39.6287	$39.63	$39.65	$39.60
Purchase #7	$140.83	10.723%	$155.9312	$155.93	$155.95	$155.90
7 purchase totals =	$1,028.14		$1,123.8812	$1,123.88	$1,123.90	$1,123.80