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	$33.40	13.106%	$37.7774	$37.78	$37.80	$37.80
Purchase #2	$137.37	3.753%	$142.5255	$142.53	$142.55	$142.50
Purchase #3	$48.46	13.722%	$55.1097	$55.11	$55.10	$55.10
Purchase #4	$169.48	13.597%	$192.5242	$192.52	$192.50	$192.50
Purchase #5	$216.60	10.383%	$239.0896	$239.09	$239.10	$239.10
Purchase #6	$143.34	8.550%	$155.5956	$155.60	$155.60	$155.60
Purchase #7	$97.28	6.211%	$103.3221	$103.32	$103.30	$103.30
7 purchase totals =	$845.93		$925.9441	$925.95	$925.95	$925.90