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	$14.27	5.548%	$15.0617	$15.06	$15.05	$15.10
Purchase #2	$64.72	12.493%	$72.8055	$72.81	$72.80	$72.80
Purchase #3	$221.97	7.512%	$238.6444	$238.64	$238.65	$238.60
Purchase #4	$142.86	9.647%	$156.6417	$156.64	$156.65	$156.60
Purchase #5	$205.71	4.251%	$214.4547	$214.45	$214.45	$214.50
Purchase #6	$187.77	11.802%	$209.9306	$209.93	$209.95	$209.90
Purchase #7	$155.70	11.348%	$173.3688	$173.37	$173.35	$173.40
7 purchase totals =	$993.00		$1,080.9074	$1,080.90	$1,080.90	$1,080.90