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	$36.80	12.757%	$41.4946	$41.49	$41.50	$41.50
Purchase #2	$103.40	6.215%	$109.8263	$109.83	$109.85	$109.80
Purchase #3	$109.47	5.428%	$115.412	$115.41	$115.40	$115.40
Purchase #4	$164.76	12.509%	$185.3698	$185.37	$185.35	$185.40
Purchase #5	$137.80	6.432%	$146.6633	$146.66	$146.65	$146.70
Purchase #6	$164.89	13.546%	$187.226	$187.23	$187.25	$187.20
Purchase #7	$103.65	13.116%	$117.2447	$117.24	$117.25	$117.20
7 purchase totals =	$820.77		$903.2367	$903.23	$903.25	$903.20