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	$40.34	9.548%	$44.1917	$44.19	$44.20	$44.20
Purchase #2	$108.56	4.222%	$113.1434	$113.14	$113.15	$113.10
Purchase #3	$132.47	7.259%	$142.086	$142.09	$142.10	$142.10
Purchase #4	$139.88	12.177%	$156.9132	$156.91	$156.90	$156.90
Purchase #5	$191.98	4.652%	$200.9109	$200.91	$200.90	$200.90
Purchase #6	$33.32	13.538%	$37.8309	$37.83	$37.85	$37.80
Purchase #7	$75.64	10.721%	$83.7494	$83.75	$83.75	$83.70
7 purchase totals =	$722.19		$778.8255	$778.82	$778.85	$778.70