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	$34.70	7.801%	$37.4069	$37.41	$37.40	$37.40
Purchase #2	$241.57	9.839%	$265.3381	$265.34	$265.35	$265.30
Purchase #3	$48.94	9.341%	$53.5115	$53.51	$53.50	$53.50
Purchase #4	$77.57	5.814%	$82.0799	$82.08	$82.10	$82.10
Purchase #5	$140.82	9.175%	$153.7402	$153.74	$153.75	$153.70
Purchase #6	$212.63	5.425%	$224.1652	$224.17	$224.15	$224.20
Purchase #7	$84.74	5.569%	$89.4592	$89.46	$89.45	$89.50
7 purchase totals =	$840.97		$905.7010	$905.71	$905.70	$905.70