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	$24.87	9.846%	$27.3187	$27.32	$27.30	$27.30
Purchase #2	$192.46	3.130%	$198.484	$198.48	$198.50	$198.50
Purchase #3	$212.91	13.410%	$241.4612	$241.46	$241.45	$241.50
Purchase #4	$165.81	4.808%	$173.7821	$173.78	$173.80	$173.80
Purchase #5	$147.67	12.635%	$166.3281	$166.33	$166.35	$166.30
Purchase #6	$223.83	13.763%	$254.6357	$254.64	$254.65	$254.60
Purchase #7	$178.56	10.105%	$196.6035	$196.60	$196.60	$196.60
7 purchase totals =	$1,146.11		$1,258.6133	$1,258.61	$1,258.65	$1,258.60