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	$53.95	7.124%	$57.7934	$57.79	$57.80	$57.80
Purchase #2	$91.28	7.636%	$98.2501	$98.25	$98.25	$98.30
Purchase #3	$38.60	4.685%	$40.4084	$40.41	$40.40	$40.40
Purchase #4	$84.80	3.186%	$87.5017	$87.50	$87.50	$87.50
Purchase #5	$38.50	5.128%	$40.4743	$40.47	$40.45	$40.50
Purchase #6	$92.54	7.735%	$99.698	$99.70	$99.70	$99.70
Purchase #7	$212.79	3.538%	$220.3185	$220.32	$220.30	$220.30
7 purchase totals =	$612.46		$644.4444	$644.44	$644.40	$644.50