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	$124.42	12.414%	$139.8655	$139.87	$139.85	$139.90
Purchase #2	$64.47	10.699%	$71.3676	$71.37	$71.35	$71.40
Purchase #3	$132.93	3.379%	$137.4217	$137.42	$137.40	$137.40
Purchase #4	$108.25	3.659%	$112.2109	$112.21	$112.20	$112.20
Purchase #5	$116.28	12.671%	$131.0138	$131.01	$131.00	$131.00
Purchase #6	$16.76	12.109%	$18.7895	$18.79	$18.80	$18.80
Purchase #7	$177.69	6.515%	$189.2665	$189.27	$189.25	$189.30
7 purchase totals =	$740.80		$799.9355	$799.94	$799.85	$800.00