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	$172.45	3.240%	$178.0374	$178.04	$178.05	$178.00
Purchase #2	$47.62	8.147%	$51.4996	$51.50	$51.50	$51.50
Purchase #3	$73.98	9.463%	$80.9807	$80.98	$81.00	$81.00
Purchase #4	$133.94	3.833%	$139.0739	$139.07	$139.05	$139.10
Purchase #5	$94.35	11.159%	$104.8785	$104.88	$104.90	$104.90
Purchase #6	$56.29	10.732%	$62.331	$62.33	$62.35	$62.30
Purchase #7	$148.31	13.177%	$167.8528	$167.85	$167.85	$167.90
7 purchase totals =	$726.94		$784.6539	$784.65	$784.70	$784.70