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	$121.73	5.606%	$128.5542	$128.55	$128.55	$128.60
Purchase #2	$107.90	3.405%	$111.574	$111.57	$111.55	$111.60
Purchase #3	$237.59	4.794%	$248.9801	$248.98	$249.00	$249.00
Purchase #4	$172.76	9.728%	$189.5661	$189.57	$189.55	$189.60
Purchase #5	$142.59	7.181%	$152.8294	$152.83	$152.85	$152.80
Purchase #6	$109.31	7.630%	$117.6504	$117.65	$117.65	$117.70
Purchase #7	$37.83	13.545%	$42.9541	$42.95	$42.95	$43.00
7 purchase totals =	$929.71		$992.1083	$992.10	$992.10	$992.30