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	$123.68	12.780%	$139.4863	$139.49	$139.50	$139.50
Purchase #2	$169.47	6.510%	$180.5025	$180.50	$180.50	$180.50
Purchase #3	$59.78	4.754%	$62.6219	$62.62	$62.60	$62.60
Purchase #4	$173.85	9.175%	$189.8007	$189.80	$189.80	$189.80
Purchase #5	$99.76	11.369%	$111.1017	$111.10	$111.10	$111.10
Purchase #6	$98.26	9.502%	$107.5967	$107.60	$107.60	$107.60
Purchase #7	$38.94	10.679%	$43.0984	$43.10	$43.10	$43.10
7 purchase totals =	$763.74		$834.2082	$834.21	$834.20	$834.20