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	$131.30	8.533%	$142.5038	$142.50	$142.50	$142.50
Purchase #2	$120.38	3.782%	$124.9328	$124.93	$124.95	$124.90
Purchase #3	$95.96	4.557%	$100.3329	$100.33	$100.35	$100.30
Purchase #4	$247.51	13.781%	$281.6194	$281.62	$281.60	$281.60
Purchase #5	$45.34	8.598%	$49.2383	$49.24	$49.25	$49.20
Purchase #6	$219.95	13.252%	$249.0978	$249.10	$249.10	$249.10
Purchase #7	$43.89	13.812%	$49.9521	$49.95	$49.95	$50.00
7 purchase totals =	$904.33		$997.6771	$997.67	$997.70	$997.60