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	$133.46	3.762%	$138.4808	$138.48	$138.50	$138.50
Purchase #2	$38.94	7.792%	$41.9742	$41.97	$41.95	$42.00
Purchase #3	$43.46	5.612%	$45.899	$45.90	$45.90	$45.90
Purchase #4	$146.72	13.328%	$166.2748	$166.27	$166.25	$166.30
Purchase #5	$44.25	11.227%	$49.2179	$49.22	$49.20	$49.20
Purchase #6	$67.43	6.466%	$71.79	$71.79	$71.80	$71.80
Purchase #7	$151.93	9.511%	$166.3801	$166.38	$166.40	$166.40
7 purchase totals =	$626.19		$680.0168	$680.01	$680.00	$680.10