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	$214.28	12.133%	$240.2786	$240.28	$240.30	$240.30
Purchase #2	$39.75	9.106%	$43.3696	$43.37	$43.35	$43.40
Purchase #3	$180.64	10.112%	$198.9063	$198.91	$198.90	$198.90
Purchase #4	$187.54	4.610%	$196.1856	$196.19	$196.20	$196.20
Purchase #5	$51.33	9.808%	$56.3644	$56.36	$56.35	$56.40
Purchase #6	$242.64	12.766%	$273.6154	$273.62	$273.60	$273.60
Purchase #7	$228.78	5.463%	$241.2783	$241.28	$241.30	$241.30
7 purchase totals =	$1,144.96		$1,249.9982	$1,250.01	$1,250.00	$1,250.10