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	$35.56	9.276%	$38.8585	$38.86	$38.85	$38.90
Purchase #2	$105.38	3.310%	$108.8681	$108.87	$108.85	$108.90
Purchase #3	$194.74	5.667%	$205.7759	$205.78	$205.80	$205.80
Purchase #4	$140.40	11.320%	$156.2933	$156.29	$156.30	$156.30
Purchase #5	$214.79	10.837%	$238.0668	$238.07	$238.05	$238.10
Purchase #6	$189.25	11.273%	$210.5842	$210.58	$210.60	$210.60
Purchase #7	$118.81	7.534%	$127.7611	$127.76	$127.75	$127.80
7 purchase totals =	$998.93		$1,086.2079	$1,086.21	$1,086.20	$1,086.40