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	$46.43	11.742%	$51.8818	$51.88	$51.90	$51.90
Purchase #2	$21.86	10.813%	$24.2237	$24.22	$24.20	$24.20
Purchase #3	$172.93	8.521%	$187.6654	$187.67	$187.65	$187.70
Purchase #4	$58.88	4.244%	$61.3789	$61.38	$61.40	$61.40
Purchase #5	$78.60	6.756%	$83.9102	$83.91	$83.90	$83.90
Purchase #6	$234.49	3.127%	$241.8225	$241.82	$241.80	$241.80
Purchase #7	$135.67	7.550%	$145.9131	$145.91	$145.90	$145.90
7 purchase totals =	$748.86		$796.7956	$796.79	$796.75	$796.80