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	$205.69	9.189%	$224.5909	$224.59	$224.60	$224.60
Purchase #2	$127.55	10.488%	$140.9274	$140.93	$140.95	$140.90
Purchase #3	$19.40	7.712%	$20.8961	$20.90	$20.90	$20.90
Purchase #4	$72.54	11.617%	$80.967	$80.97	$80.95	$81.00
Purchase #5	$182.77	9.676%	$200.4548	$200.45	$200.45	$200.50
Purchase #6	$7.60	10.871%	$8.4262	$8.43	$8.45	$8.40
Purchase #7	$46.91	10.651%	$51.9064	$51.91	$51.90	$51.90
7 purchase totals =	$662.46		$728.1688	$728.18	$728.20	$728.20