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	$141.59	13.204%	$160.2855	$160.29	$160.30	$160.30
Purchase #2	$91.71	6.790%	$97.9371	$97.94	$97.95	$97.90
Purchase #3	$210.61	13.411%	$238.8549	$238.85	$238.85	$238.90
Purchase #4	$7.51	4.634%	$7.858	$7.86	$7.85	$7.90
Purchase #5	$180.65	8.507%	$196.0179	$196.02	$196.00	$196.00
Purchase #6	$145.81	10.690%	$161.3971	$161.40	$161.40	$161.40
Purchase #7	$151.95	3.284%	$156.94	$156.94	$156.95	$156.90
7 purchase totals =	$929.83		$1,019.2905	$1,019.30	$1,019.30	$1,019.30