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	$72.89	11.570%	$81.3234	$81.32	$81.30	$81.30
Purchase #2	$123.94	3.282%	$128.0077	$128.01	$128.00	$128.00
Purchase #3	$38.76	11.638%	$43.2709	$43.27	$43.25	$43.30
Purchase #4	$17.60	9.585%	$19.287	$19.29	$19.30	$19.30
Purchase #5	$241.78	12.437%	$271.8502	$271.85	$271.85	$271.90
Purchase #6	$250.48	9.110%	$273.2987	$273.30	$273.30	$273.30
Purchase #7	$40.88	4.204%	$42.5986	$42.60	$42.60	$42.60
7 purchase totals =	$786.33		$859.6365	$859.64	$859.60	$859.70