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	$155.78	12.263%	$174.8833	$174.88	$174.90	$174.90
Purchase #2	$205.37	8.482%	$222.7895	$222.79	$222.80	$222.80
Purchase #3	$107.52	9.622%	$117.8656	$117.87	$117.85	$117.90
Purchase #4	$148.93	11.628%	$166.2476	$166.25	$166.25	$166.20
Purchase #5	$73.34	13.298%	$83.0928	$83.09	$83.10	$83.10
Purchase #6	$76.87	12.693%	$86.6271	$86.63	$86.65	$86.60
Purchase #7	$150.60	13.601%	$171.0831	$171.08	$171.10	$171.10
7 purchase totals =	$918.41		$1,022.5890	$1,022.59	$1,022.65	$1,022.60