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	$142.58	9.514%	$156.1451	$156.15	$156.15	$156.10
Purchase #2	$189.52	3.709%	$196.5493	$196.55	$196.55	$196.50
Purchase #3	$139.57	13.419%	$158.2989	$158.30	$158.30	$158.30
Purchase #4	$70.28	3.590%	$72.8031	$72.80	$72.80	$72.80
Purchase #5	$198.28	13.280%	$224.6116	$224.61	$224.60	$224.60
Purchase #6	$32.62	7.348%	$35.0169	$35.02	$35.00	$35.00
Purchase #7	$7.40	7.230%	$7.935	$7.94	$7.95	$7.90
7 purchase totals =	$780.25		$851.3599	$851.37	$851.35	$851.20