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	$19.73	3.569%	$20.4342	$20.43	$20.45	$20.40
Purchase #2	$41.61	12.659%	$46.8774	$46.88	$46.90	$46.90
Purchase #3	$168.37	10.741%	$186.4546	$186.45	$186.45	$186.50
Purchase #4	$231.35	12.295%	$259.7945	$259.79	$259.80	$259.80
Purchase #5	$152.56	7.623%	$164.1896	$164.19	$164.20	$164.20
Purchase #6	$215.32	9.823%	$236.4709	$236.47	$236.45	$236.50
Purchase #7	$245.53	8.275%	$265.8476	$265.85	$265.85	$265.80
7 purchase totals =	$1,074.47		$1,180.0688	$1,180.06	$1,180.10	$1,180.10