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	$28.90	10.346%	$31.89	$31.89	$31.90	$31.90
Purchase #2	$166.56	5.368%	$175.5009	$175.50	$175.50	$175.50
Purchase #3	$98.30	5.308%	$103.5178	$103.52	$103.50	$103.50
Purchase #4	$135.88	11.557%	$151.5837	$151.58	$151.60	$151.60
Purchase #5	$208.81	10.187%	$230.0815	$230.08	$230.10	$230.10
Purchase #6	$66.90	13.724%	$76.0814	$76.08	$76.10	$76.10
Purchase #7	$70.29	4.690%	$73.5866	$73.59	$73.60	$73.60
7 purchase totals =	$775.64		$842.2419	$842.24	$842.30	$842.30