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	$19.38	7.655%	$20.8635	$20.86	$20.85	$20.90
Purchase #2	$54.95	11.708%	$61.3835	$61.38	$61.40	$61.40
Purchase #3	$138.29	3.242%	$142.7734	$142.77	$142.75	$142.80
Purchase #4	$34.58	3.661%	$35.846	$35.85	$35.85	$35.80
Purchase #5	$204.63	9.689%	$224.4566	$224.46	$224.45	$224.50
Purchase #6	$111.59	12.242%	$125.2508	$125.25	$125.25	$125.30
Purchase #7	$151.94	9.643%	$166.5916	$166.59	$166.60	$166.60
7 purchase totals =	$715.36		$777.1654	$777.16	$777.15	$777.30