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	$69.52	5.463%	$73.3179	$73.32	$73.30	$73.30
Purchase #2	$9.37	13.105%	$10.5979	$10.60	$10.60	$10.60
Purchase #3	$84.31	7.274%	$90.4427	$90.44	$90.45	$90.40
Purchase #4	$180.75	5.874%	$191.3673	$191.37	$191.35	$191.40
Purchase #5	$242.68	11.217%	$269.9014	$269.90	$269.90	$269.90
Purchase #6	$111.80	11.312%	$124.4468	$124.45	$124.45	$124.40
Purchase #7	$67.28	3.821%	$69.8508	$69.85	$69.85	$69.90
7 purchase totals =	$765.71		$829.9248	$829.93	$829.90	$829.90