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	$19.39	7.307%	$20.8068	$20.81	$20.80	$20.80
Purchase #2	$133.71	7.756%	$144.0805	$144.08	$144.10	$144.10
Purchase #3	$211.97	12.332%	$238.1101	$238.11	$238.10	$238.10
Purchase #4	$54.46	8.361%	$59.0134	$59.01	$59.00	$59.00
Purchase #5	$35.34	6.822%	$37.7509	$37.75	$37.75	$37.80
Purchase #6	$142.92	5.724%	$151.1007	$151.10	$151.10	$151.10
Purchase #7	$31.62	3.234%	$32.6426	$32.64	$32.65	$32.60
7 purchase totals =	$629.41		$683.5050	$683.50	$683.50	$683.50