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	$100.99	12.404%	$113.5168	$113.52	$113.50	$113.50
Purchase #2	$16.75	10.388%	$18.49	$18.49	$18.50	$18.50
Purchase #3	$24.96	10.257%	$27.5201	$27.52	$27.50	$27.50
Purchase #4	$185.90	3.649%	$192.6835	$192.68	$192.70	$192.70
Purchase #5	$242.83	7.392%	$260.78	$260.78	$260.80	$260.80
Purchase #6	$35.35	5.500%	$37.2943	$37.29	$37.30	$37.30
Purchase #7	$90.96	10.664%	$100.66	$100.66	$100.65	$100.70
7 purchase totals =	$697.74		$750.9447	$750.94	$750.95	$751.00