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	$42.99	10.239%	$47.3917	$47.39	$47.40	$47.40
Purchase #2	$48.56	4.790%	$50.886	$50.89	$50.90	$50.90
Purchase #3	$174.26	10.140%	$191.93	$191.93	$191.95	$191.90
Purchase #4	$36.47	5.354%	$38.4226	$38.42	$38.40	$38.40
Purchase #5	$228.89	11.627%	$255.503	$255.50	$255.50	$255.50
Purchase #6	$203.35	9.446%	$222.5584	$222.56	$222.55	$222.60
Purchase #7	$97.30	3.815%	$101.012	$101.01	$101.00	$101.00
7 purchase totals =	$831.82		$907.7037	$907.70	$907.70	$907.70