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	$23.93	6.662%	$25.5242	$25.52	$25.50	$25.50
Purchase #2	$213.28	3.795%	$221.374	$221.37	$221.35	$221.40
Purchase #3	$35.68	10.839%	$39.5474	$39.55	$39.55	$39.50
Purchase #4	$37.65	11.762%	$42.0784	$42.08	$42.10	$42.10
Purchase #5	$31.30	7.493%	$33.6453	$33.65	$33.65	$33.60
Purchase #6	$55.33	8.138%	$59.8328	$59.83	$59.85	$59.80
Purchase #7	$72.64	9.225%	$79.341	$79.34	$79.35	$79.30
7 purchase totals =	$469.81		$501.3431	$501.34	$501.35	$501.20