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	$38.67	4.795%	$40.5242	$40.52	$40.50	$40.50
Purchase #2	$132.76	10.777%	$147.0675	$147.07	$147.05	$147.10
Purchase #3	$65.26	11.826%	$72.9776	$72.98	$73.00	$73.00
Purchase #4	$89.65	12.300%	$100.677	$100.68	$100.70	$100.70
Purchase #5	$222.93	7.808%	$240.3364	$240.34	$240.35	$240.30
Purchase #6	$35.64	5.647%	$37.6526	$37.65	$37.65	$37.70
Purchase #7	$183.69	8.855%	$199.9557	$199.96	$199.95	$200.00
7 purchase totals =	$768.60		$839.1910	$839.20	$839.20	$839.30