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	$140.44	12.857%	$158.4964	$158.50	$158.50	$158.50
Purchase #2	$112.60	11.850%	$125.9431	$125.94	$125.95	$125.90
Purchase #3	$127.29	4.193%	$132.6273	$132.63	$132.65	$132.60
Purchase #4	$222.82	8.423%	$241.5881	$241.59	$241.60	$241.60
Purchase #5	$20.76	4.310%	$21.6548	$21.65	$21.65	$21.70
Purchase #6	$217.62	11.290%	$242.1893	$242.19	$242.20	$242.20
Purchase #7	$199.25	11.854%	$222.8691	$222.87	$222.85	$222.90
7 purchase totals =	$1,040.78		$1,145.3681	$1,145.37	$1,145.40	$1,145.40