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	$44.85	13.729%	$51.0075	$51.01	$51.00	$51.00
Purchase #2	$75.42	4.203%	$78.5899	$78.59	$78.60	$78.60
Purchase #3	$141.77	12.427%	$159.3878	$159.39	$159.40	$159.40
Purchase #4	$31.65	6.485%	$33.7025	$33.70	$33.70	$33.70
Purchase #5	$35.80	4.770%	$37.5077	$37.51	$37.50	$37.50
Purchase #6	$139.64	13.861%	$158.9955	$159.00	$159.00	$159.00
Purchase #7	$30.43	13.513%	$34.542	$34.54	$34.55	$34.50
7 purchase totals =	$499.56		$553.7329	$553.74	$553.75	$553.70