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	$232.86	9.649%	$255.3287	$255.33	$255.35	$255.30
Purchase #2	$220.60	8.799%	$240.0106	$240.01	$240.00	$240.00
Purchase #3	$19.89	9.214%	$21.7227	$21.72	$21.70	$21.70
Purchase #4	$45.44	7.467%	$48.833	$48.83	$48.85	$48.80
Purchase #5	$193.35	12.542%	$217.6	$217.60	$217.60	$217.60
Purchase #6	$72.95	13.428%	$82.7457	$82.75	$82.75	$82.70
Purchase #7	$45.64	12.508%	$51.3487	$51.35	$51.35	$51.30
7 purchase totals =	$830.73		$917.5894	$917.59	$917.60	$917.40