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	$246.59	11.700%	$275.441	$275.44	$275.45	$275.40
Purchase #2	$138.50	11.655%	$154.6422	$154.64	$154.65	$154.60
Purchase #3	$156.68	3.349%	$161.9272	$161.93	$161.95	$161.90
Purchase #4	$119.51	3.466%	$123.6522	$123.65	$123.65	$123.70
Purchase #5	$168.37	8.209%	$182.1915	$182.19	$182.20	$182.20
Purchase #6	$228.83	5.243%	$240.8276	$240.83	$240.85	$240.80
Purchase #7	$96.89	7.247%	$103.9116	$103.91	$103.90	$103.90
7 purchase totals =	$1,155.37		$1,242.5933	$1,242.59	$1,242.65	$1,242.50