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	$51.34	6.368%	$54.6093	$54.61	$54.60	$54.60
Purchase #2	$136.45	3.170%	$140.7755	$140.78	$140.80	$140.80
Purchase #3	$141.51	6.239%	$150.3388	$150.34	$150.35	$150.30
Purchase #4	$218.46	4.471%	$228.2273	$228.23	$228.25	$228.20
Purchase #5	$186.79	9.781%	$205.0599	$205.06	$205.05	$205.10
Purchase #6	$72.54	11.448%	$80.8444	$80.84	$80.85	$80.80
Purchase #7	$132.32	9.521%	$144.9182	$144.92	$144.90	$144.90
7 purchase totals =	$939.41		$1,004.7734	$1,004.78	$1,004.80	$1,004.70