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	$90.50	3.117%	$93.3209	$93.32	$93.30	$93.30
Purchase #2	$117.36	5.483%	$123.7948	$123.79	$123.80	$123.80
Purchase #3	$108.52	11.784%	$121.308	$121.31	$121.30	$121.30
Purchase #4	$69.78	12.270%	$78.342	$78.34	$78.35	$78.30
Purchase #5	$234.76	9.410%	$256.8509	$256.85	$256.85	$256.90
Purchase #6	$155.57	10.514%	$171.9266	$171.93	$171.95	$171.90
Purchase #7	$80.71	4.515%	$84.3541	$84.35	$84.35	$84.40
7 purchase totals =	$857.20		$929.8973	$929.89	$929.90	$929.90