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	$113.78	13.749%	$129.4236	$129.42	$129.40	$129.40
Purchase #2	$23.57	3.495%	$24.3938	$24.39	$24.40	$24.40
Purchase #3	$45.58	10.699%	$50.4566	$50.46	$50.45	$50.50
Purchase #4	$163.55	13.651%	$185.8762	$185.88	$185.90	$185.90
Purchase #5	$138.97	6.730%	$148.3227	$148.32	$148.30	$148.30
Purchase #6	$148.39	13.484%	$168.3989	$168.40	$168.40	$168.40
Purchase #7	$183.88	10.645%	$203.454	$203.45	$203.45	$203.50
7 purchase totals =	$817.72		$910.3258	$910.32	$910.30	$910.40