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	$132.78	5.817%	$140.5038	$140.50	$140.50	$140.50
Purchase #2	$139.85	6.154%	$148.4564	$148.46	$148.45	$148.50
Purchase #3	$114.27	4.393%	$119.2899	$119.29	$119.30	$119.30
Purchase #4	$168.78	12.161%	$189.3053	$189.31	$189.30	$189.30
Purchase #5	$37.70	4.511%	$39.4006	$39.40	$39.40	$39.40
Purchase #6	$35.31	11.306%	$39.3021	$39.30	$39.30	$39.30
Purchase #7	$128.45	10.794%	$142.3149	$142.31	$142.30	$142.30
7 purchase totals =	$757.14		$818.5730	$818.57	$818.55	$818.60