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	$70.49	11.459%	$78.5674	$78.57	$78.55	$78.60
Purchase #2	$141.48	12.738%	$159.5017	$159.50	$159.50	$159.50
Purchase #3	$162.30	6.161%	$172.2993	$172.30	$172.30	$172.30
Purchase #4	$185.32	3.573%	$191.9415	$191.94	$191.95	$191.90
Purchase #5	$228.30	4.188%	$237.8612	$237.86	$237.85	$237.90
Purchase #6	$21.40	7.612%	$23.029	$23.03	$23.05	$23.00
Purchase #7	$41.80	9.724%	$45.8646	$45.86	$45.85	$45.90
7 purchase totals =	$851.09		$909.0647	$909.06	$909.05	$909.10