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	$233.48	3.469%	$241.5794	$241.58	$241.60	$241.60
Purchase #2	$34.43	12.633%	$38.7795	$38.78	$38.80	$38.80
Purchase #3	$211.93	6.616%	$225.9513	$225.95	$225.95	$226.00
Purchase #4	$148.77	7.185%	$159.4591	$159.46	$159.45	$159.50
Purchase #5	$160.38	7.187%	$171.9065	$171.91	$171.90	$171.90
Purchase #6	$43.48	7.268%	$46.6401	$46.64	$46.65	$46.60
Purchase #7	$95.54	4.692%	$100.0227	$100.02	$100.00	$100.00
7 purchase totals =	$928.01		$984.3386	$984.34	$984.35	$984.40