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	$33.95	10.241%	$37.4268	$37.43	$37.45	$37.40
Purchase #2	$240.78	10.362%	$265.7296	$265.73	$265.75	$265.70
Purchase #3	$160.81	4.766%	$168.4742	$168.47	$168.45	$168.50
Purchase #4	$32.68	8.294%	$35.3905	$35.39	$35.40	$35.40
Purchase #5	$13.85	3.265%	$14.3022	$14.30	$14.30	$14.30
Purchase #6	$32.57	9.423%	$35.6391	$35.64	$35.65	$35.60
Purchase #7	$68.59	4.864%	$71.9262	$71.93	$71.95	$71.90
7 purchase totals =	$583.23		$628.8886	$628.89	$628.95	$628.80