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	$23.76	6.544%	$25.3149	$25.31	$25.30	$25.30
Purchase #2	$48.51	9.267%	$53.0054	$53.01	$53.00	$53.00
Purchase #3	$98.84	12.799%	$111.4905	$111.49	$111.50	$111.50
Purchase #4	$176.71	10.772%	$195.7452	$195.75	$195.75	$195.70
Purchase #5	$187.57	6.373%	$199.5238	$199.52	$199.50	$199.50
Purchase #6	$242.83	8.581%	$263.6672	$263.67	$263.65	$263.70
Purchase #7	$108.87	13.425%	$123.4858	$123.49	$123.50	$123.50
7 purchase totals =	$887.09		$972.2328	$972.24	$972.20	$972.20