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	$241.40	12.300%	$271.0922	$271.09	$271.10	$271.10
Purchase #2	$113.27	4.576%	$118.4532	$118.45	$118.45	$118.50
Purchase #3	$31.65	13.581%	$35.9484	$35.95	$35.95	$35.90
Purchase #4	$178.77	10.138%	$196.8937	$196.89	$196.90	$196.90
Purchase #5	$44.42	4.715%	$46.5144	$46.51	$46.50	$46.50
Purchase #6	$182.38	12.172%	$204.5793	$204.58	$204.60	$204.60
Purchase #7	$41.35	7.229%	$44.3392	$44.34	$44.35	$44.30
7 purchase totals =	$833.24		$917.8204	$917.81	$917.85	$917.80