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	$96.73	7.402%	$103.89	$103.89	$103.90	$103.90
Purchase #2	$162.94	9.154%	$177.8555	$177.86	$177.85	$177.90
Purchase #3	$182.47	7.686%	$196.4946	$196.49	$196.50	$196.50
Purchase #4	$64.49	12.480%	$72.5384	$72.54	$72.55	$72.50
Purchase #5	$20.51	3.260%	$21.1786	$21.18	$21.20	$21.20
Purchase #6	$131.30	6.167%	$139.3973	$139.40	$139.40	$139.40
Purchase #7	$174.75	7.276%	$187.4648	$187.46	$187.45	$187.50
7 purchase totals =	$833.19		$898.8192	$898.82	$898.85	$898.90